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 $60.32   13.363%   $68.3806   $68.38   $68.40   $68.40  
  Purchase #2 $111.65   12.495%   $125.6007   $125.60   $125.60   $125.60  
  Purchase #3 $165.49   10.644%   $183.1048   $183.10   $183.10   $183.10  
  Purchase #4 $101.76   6.718%   $108.5962   $108.60   $108.60   $108.60  
  Purchase #5 $78.56   8.770%   $85.4497   $85.45   $85.45   $85.40  
  Purchase #6 $24.29   6.659%   $25.9075   $25.91   $25.90   $25.90  
  Purchase #7 $103.97   5.199%   $109.3754   $109.38   $109.40   $109.40  
  7 purchase totals = $646.04       $706.4149   $706.42   $706.45   $706.40