Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.25   12.407%   $268.9337   $268.93   $268.95   $268.90  
  Purchase #2 $208.57   11.403%   $232.3532   $232.35   $232.35   $232.40  
  Purchase #3 $183.71   9.731%   $201.5868   $201.59   $201.60   $201.60  
  Purchase #4 $137.58   10.717%   $152.3244   $152.32   $152.30   $152.30  
  Purchase #5 $231.53   11.655%   $258.5148   $258.51   $258.50   $258.50  
  Purchase #6 $182.36   10.563%   $201.6227   $201.62   $201.60   $201.60  
  Purchase #7 $105.28   10.666%   $116.5092   $116.51   $116.50   $116.50  
  7 purchase totals = $1,288.28       $1,431.8448   $1,431.83   $1,431.80   $1,431.80