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 $63.28   4.620%   $66.2035   $66.20   $66.20   $66.20  
  Purchase #2 $208.76   12.348%   $234.5377   $234.54   $234.55   $234.50  
  Purchase #3 $17.49   7.232%   $18.7549   $18.75   $18.75   $18.80  
  Purchase #4 $116.46   9.354%   $127.3537   $127.35   $127.35   $127.40  
  Purchase #5 $67.61   4.414%   $70.5943   $70.59   $70.60   $70.60  
  Purchase #6 $62.90   12.352%   $70.6694   $70.67   $70.65   $70.70  
  Purchase #7 $17.60   12.804%   $19.8535   $19.85   $19.85   $19.90  
  7 purchase totals = $554.10       $607.9670   $607.95   $607.95   $608.10