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 $197.47   8.761%   $214.7703   $214.77   $214.75   $214.80  
  Purchase #2 $52.28   9.419%   $57.2043   $57.20   $57.20   $57.20  
  Purchase #3 $52.92   3.561%   $54.8045   $54.80   $54.80   $54.80  
  Purchase #4 $44.42   7.785%   $47.8781   $47.88   $47.90   $47.90  
  Purchase #5 $57.83   9.618%   $63.3921   $63.39   $63.40   $63.40  
  Purchase #6 $82.28   7.260%   $88.2535   $88.25   $88.25   $88.30  
  Purchase #7 $172.57   9.672%   $189.261   $189.26   $189.25   $189.30  
  7 purchase totals = $659.77       $715.5638   $715.55   $715.55   $715.70