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 $58.68   5.486%   $61.8992   $61.90   $61.90   $61.90  
  Purchase #2 $85.61   9.290%   $93.5632   $93.56   $93.55   $93.60  
  Purchase #3 $188.78   6.142%   $200.3749   $200.37   $200.35   $200.40  
  Purchase #4 $26.44   9.326%   $28.9058   $28.91   $28.90   $28.90  
  Purchase #5 $139.32   10.644%   $154.1492   $154.15   $154.15   $154.10  
  Purchase #6 $49.70   3.672%   $51.525   $51.53   $51.55   $51.50  
  Purchase #7 $87.49   8.164%   $94.6327   $94.63   $94.65   $94.60  
  7 purchase totals = $636.02       $685.0500   $685.05   $685.05   $685.00