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 $182.46   11.590%   $203.6071   $203.61   $203.60   $203.60  
  Purchase #2 $23.47   8.747%   $25.5229   $25.52   $25.50   $25.50  
  Purchase #3 $88.55   11.752%   $98.9564   $98.96   $98.95   $99.00  
  Purchase #4 $180.54   13.304%   $204.559   $204.56   $204.55   $204.60  
  Purchase #5 $35.48   3.740%   $36.807   $36.81   $36.80   $36.80  
  Purchase #6 $176.88   8.380%   $191.7025   $191.70   $191.70   $191.70  
  Purchase #7 $119.99   5.307%   $126.3579   $126.36   $126.35   $126.40  
  7 purchase totals = $807.37       $887.5128   $887.52   $887.45   $887.60