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 $25.46   4.833%   $26.6905   $26.69   $26.70   $26.70  
  Purchase #2 $183.83   5.683%   $194.2771   $194.28   $194.30   $194.30  
  Purchase #3 $64.32   11.356%   $71.6242   $71.62   $71.60   $71.60  
  Purchase #4 $65.98   6.307%   $70.1414   $70.14   $70.15   $70.10  
  Purchase #5 $144.56   8.735%   $157.1873   $157.19   $157.20   $157.20  
  Purchase #6 $7.31   11.790%   $8.1718   $8.17   $8.15   $8.20  
  Purchase #7 $177.96   11.160%   $197.8203   $197.82   $197.80   $197.80  
  7 purchase totals = $669.42       $725.9126   $725.91   $725.90   $725.90