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 $61.93   6.753%   $66.1121   $66.11   $66.10   $66.10  
  Purchase #2 $131.71   7.475%   $141.5553   $141.56   $141.55   $141.60  
  Purchase #3 $116.62   3.359%   $120.5373   $120.54   $120.55   $120.50  
  Purchase #4 $125.38   13.192%   $141.9201   $141.92   $141.90   $141.90  
  Purchase #5 $238.48   11.173%   $265.1254   $265.13   $265.15   $265.10  
  Purchase #6 $14.82   12.455%   $16.6658   $16.67   $16.65   $16.70  
  Purchase #7 $88.27   7.271%   $94.6881   $94.69   $94.70   $94.70  
  7 purchase totals = $777.21       $846.6041   $846.62   $846.60   $846.60