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 $55.56   10.198%   $61.226   $61.23   $61.25   $61.20  
  Purchase #2 $109.54   5.650%   $115.729   $115.73   $115.75   $115.70  
  Purchase #3 $22.33   5.256%   $23.5037   $23.50   $23.50   $23.50  
  Purchase #4 $149.96   7.164%   $160.7031   $160.70   $160.70   $160.70  
  Purchase #5 $105.81   8.701%   $115.0165   $115.02   $115.00   $115.00  
  Purchase #6 $68.37   6.340%   $72.7047   $72.70   $72.70   $72.70  
  Purchase #7 $234.96   13.290%   $266.1862   $266.19   $266.20   $266.20  
  7 purchase totals = $746.53       $815.0692   $815.07   $815.10   $815.00