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 $65.78   11.258%   $73.1855   $73.19   $73.20   $73.20  
  Purchase #2 $39.31   8.356%   $42.5947   $42.59   $42.60   $42.60  
  Purchase #3 $82.48   12.468%   $92.7636   $92.76   $92.75   $92.80  
  Purchase #4 $120.75   7.473%   $129.7736   $129.77   $129.75   $129.80  
  Purchase #5 $93.49   9.369%   $102.2491   $102.25   $102.25   $102.20  
  Purchase #6 $53.73   12.207%   $60.2888   $60.29   $60.30   $60.30  
  Purchase #7 $77.36   12.583%   $87.0942   $87.09   $87.10   $87.10  
  7 purchase totals = $532.90       $587.9495   $587.94   $587.95   $588.00