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 $86.83   8.864%   $94.5266   $94.53   $94.55   $94.50  
  Purchase #2 $44.97   11.493%   $50.1384   $50.14   $50.15   $50.10  
  Purchase #3 $153.61   10.388%   $169.567   $169.57   $169.55   $169.60  
  Purchase #4 $105.63   10.437%   $116.6546   $116.65   $116.65   $116.70  
  Purchase #5 $41.61   7.203%   $44.6072   $44.61   $44.60   $44.60  
  Purchase #6 $126.96   5.775%   $134.2919   $134.29   $134.30   $134.30  
  Purchase #7 $86.81   6.460%   $92.4179   $92.42   $92.40   $92.40  
  7 purchase totals = $646.42       $702.2036   $702.21   $702.20   $702.20