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 $85.71   8.536%   $93.0262   $93.03   $93.05   $93.00  
  Purchase #2 $218.81   12.583%   $246.3429   $246.34   $246.35   $246.30  
  Purchase #3 $18.63   7.613%   $20.0483   $20.05   $20.05   $20.00  
  Purchase #4 $125.85   13.436%   $142.7592   $142.76   $142.75   $142.80  
  Purchase #5 $100.96   6.425%   $107.4467   $107.45   $107.45   $107.40  
  Purchase #6 $162.62   11.742%   $181.7148   $181.71   $181.70   $181.70  
  Purchase #7 $96.49   6.488%   $102.7503   $102.75   $102.75   $102.80  
  7 purchase totals = $809.07       $894.0884   $894.09   $894.10   $894.00