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 $47.67   6.161%   $50.6069   $50.61   $50.60   $50.60  
  Purchase #2 $61.64   5.143%   $64.8101   $64.81   $64.80   $64.80  
  Purchase #3 $113.42   5.507%   $119.666   $119.67   $119.65   $119.70  
  Purchase #4 $108.95   6.638%   $116.1821   $116.18   $116.20   $116.20  
  Purchase #5 $83.69   6.552%   $89.1734   $89.17   $89.15   $89.20  
  Purchase #6 $46.80   6.581%   $49.8799   $49.88   $49.90   $49.90  
  Purchase #7 $184.90   11.394%   $205.9675   $205.97   $205.95   $206.00  
  7 purchase totals = $647.07       $696.2859   $696.29   $696.25   $696.40