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 $165.73   12.219%   $185.9805   $185.98   $186.00   $186.00  
  Purchase #2 $9.77   10.133%   $10.76   $10.76   $10.75   $10.80  
  Purchase #3 $123.55   7.602%   $132.9423   $132.94   $132.95   $132.90  
  Purchase #4 $58.59   3.427%   $60.5979   $60.60   $60.60   $60.60  
  Purchase #5 $148.66   3.465%   $153.8111   $153.81   $153.80   $153.80  
  Purchase #6 $112.50   4.141%   $117.1586   $117.16   $117.15   $117.20  
  Purchase #7 $48.68   7.447%   $52.3052   $52.31   $52.30   $52.30  
  7 purchase totals = $667.48       $713.5556   $713.56   $713.55   $713.60