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 $196.93   11.228%   $219.0413   $219.04   $219.05   $219.00  
  Purchase #2 $195.70   4.434%   $204.3773   $204.38   $204.40   $204.40  
  Purchase #3 $182.47   9.588%   $199.9652   $199.97   $199.95   $200.00  
  Purchase #4 $112.55   4.382%   $117.4819   $117.48   $117.50   $117.50  
  Purchase #5 $56.86   10.619%   $62.898   $62.90   $62.90   $62.90  
  Purchase #6 $32.91   5.728%   $34.7951   $34.80   $34.80   $34.80  
  Purchase #7 $91.59   11.453%   $102.0798   $102.08   $102.10   $102.10  
  7 purchase totals = $869.01       $940.6386   $940.65   $940.70   $940.70