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 $184.83   13.455%   $209.6989   $209.70   $209.70   $209.70  
  Purchase #2 $113.44   8.137%   $122.6706   $122.67   $122.65   $122.70  
  Purchase #3 $46.75   11.138%   $51.957   $51.96   $51.95   $52.00  
  Purchase #4 $92.75   12.349%   $104.2037   $104.20   $104.20   $104.20  
  Purchase #5 $233.87   7.411%   $251.2021   $251.20   $251.20   $251.20  
  Purchase #6 $187.52   5.373%   $197.5954   $197.60   $197.60   $197.60  
  Purchase #7 $13.49   13.137%   $15.2622   $15.26   $15.25   $15.30  
  7 purchase totals = $872.65       $952.5899   $952.59   $952.55   $952.70