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 $66.92   7.508%   $71.9444   $71.94   $71.95   $71.90  
  Purchase #2 $201.26   8.504%   $218.3752   $218.38   $218.40   $218.40  
  Purchase #3 $59.51   7.541%   $63.9976   $64.00   $64.00   $64.00  
  Purchase #4 $12.90   11.291%   $14.3565   $14.36   $14.35   $14.40  
  Purchase #5 $155.82   4.357%   $162.6091   $162.61   $162.60   $162.60  
  Purchase #6 $111.93   3.465%   $115.8084   $115.81   $115.80   $115.80  
  Purchase #7 $186.52   6.814%   $199.2295   $199.23   $199.25   $199.20  
  7 purchase totals = $794.86       $846.3207   $846.33   $846.35   $846.30