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 $92.92   12.590%   $104.6186   $104.62   $104.60   $104.60  
  Purchase #2 $68.94   4.400%   $71.9734   $71.97   $71.95   $72.00  
  Purchase #3 $152.98   5.381%   $161.2119   $161.21   $161.20   $161.20  
  Purchase #4 $151.82   3.526%   $157.1732   $157.17   $157.15   $157.20  
  Purchase #5 $177.25   5.275%   $186.5999   $186.60   $186.60   $186.60  
  Purchase #6 $53.68   12.437%   $60.3562   $60.36   $60.35   $60.40  
  Purchase #7 $229.27   6.858%   $244.9933   $244.99   $245.00   $245.00  
  7 purchase totals = $926.86       $986.9265   $986.92   $986.85   $987.00