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 $107.77   8.443%   $116.869   $116.87   $116.85   $116.90  
  Purchase #2 $197.38   5.199%   $207.6418   $207.64   $207.65   $207.60  
  Purchase #3 $205.32   3.341%   $212.1797   $212.18   $212.20   $212.20  
  Purchase #4 $30.25   9.769%   $33.2051   $33.21   $33.20   $33.20  
  Purchase #5 $10.93   7.287%   $11.7265   $11.73   $11.75   $11.70  
  Purchase #6 $196.50   7.775%   $211.7779   $211.78   $211.80   $211.80  
  Purchase #7 $153.46   11.335%   $170.8547   $170.85   $170.85   $170.90  
  7 purchase totals = $901.61       $964.2547   $964.26   $964.30   $964.30