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 $16.25   6.446%   $17.2975   $17.30   $17.30   $17.30  
  Purchase #2 $136.25   8.341%   $147.6146   $147.61   $147.60   $147.60  
  Purchase #3 $236.52   5.438%   $249.382   $249.38   $249.40   $249.40  
  Purchase #4 $126.74   11.304%   $141.0667   $141.07   $141.05   $141.10  
  Purchase #5 $227.93   5.709%   $240.9425   $240.94   $240.95   $240.90  
  Purchase #6 $18.59   6.560%   $19.8095   $19.81   $19.80   $19.80  
  Purchase #7 $202.37   8.543%   $219.6585   $219.66   $219.65   $219.70  
  7 purchase totals = $964.65       $1,035.7713   $1,035.77   $1,035.75   $1,035.80