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 $191.68   9.383%   $209.6653   $209.67   $209.65   $209.70  
  Purchase #2 $32.56   10.537%   $35.9908   $35.99   $36.00   $36.00  
  Purchase #3 $52.76   4.268%   $55.0118   $55.01   $55.00   $55.00  
  Purchase #4 $202.42   13.817%   $230.3884   $230.39   $230.40   $230.40  
  Purchase #5 $59.59   7.676%   $64.1641   $64.16   $64.15   $64.20  
  Purchase #6 $142.89   13.115%   $161.63   $161.63   $161.65   $161.60  
  Purchase #7 $132.39   13.550%   $150.3288   $150.33   $150.35   $150.30  
  7 purchase totals = $814.29       $907.1792   $907.18   $907.20   $907.20