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 $58.75   4.852%   $61.6006   $61.60   $61.60   $61.60  
  Purchase #2 $161.72   11.259%   $179.9281   $179.93   $179.95   $179.90  
  Purchase #3 $217.38   9.191%   $237.3594   $237.36   $237.35   $237.40  
  Purchase #4 $210.35   13.246%   $238.213   $238.21   $238.20   $238.20  
  Purchase #5 $38.56   11.634%   $43.0461   $43.05   $43.05   $43.00  
  Purchase #6 $22.35   12.354%   $25.1111   $25.11   $25.10   $25.10  
  Purchase #7 $6.73   7.548%   $7.238   $7.24   $7.25   $7.20  
  7 purchase totals = $715.84       $792.4963   $792.50   $792.50   $792.40