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 $67.42   12.696%   $75.9796   $75.98   $76.00   $76.00  
  Purchase #2 $173.82   9.699%   $190.6788   $190.68   $190.70   $190.70  
  Purchase #3 $111.73   9.828%   $122.7108   $122.71   $122.70   $122.70  
  Purchase #4 $46.94   4.838%   $49.211   $49.21   $49.20   $49.20  
  Purchase #5 $234.98   3.609%   $243.4604   $243.46   $243.45   $243.50  
  Purchase #6 $25.45   7.517%   $27.3631   $27.36   $27.35   $27.40  
  Purchase #7 $55.83   5.327%   $58.8041   $58.80   $58.80   $58.80  
  7 purchase totals = $716.17       $768.2078   $768.20   $768.20   $768.30