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 $176.97   3.263%   $182.7445   $182.74   $182.75   $182.70  
  Purchase #2 $224.69   3.448%   $232.4373   $232.44   $232.45   $232.40  
  Purchase #3 $154.56   12.279%   $173.5384   $173.54   $173.55   $173.50  
  Purchase #4 $110.88   11.763%   $123.9228   $123.92   $123.90   $123.90  
  Purchase #5 $208.75   13.255%   $236.4198   $236.42   $236.40   $236.40  
  Purchase #6 $241.51   4.305%   $251.907   $251.91   $251.90   $251.90  
  Purchase #7 $26.57   11.142%   $29.5304   $29.53   $29.55   $29.50  
  7 purchase totals = $1,143.93       $1,230.5002   $1,230.50   $1,230.50   $1,230.30