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 $60.65   10.771%   $67.1826   $67.18   $67.20   $67.20  
  Purchase #2 $215.64   13.536%   $244.829   $244.83   $244.85   $244.80  
  Purchase #3 $67.94   10.386%   $74.9962   $75.00   $75.00   $75.00  
  Purchase #4 $146.56   4.425%   $153.0453   $153.05   $153.05   $153.00  
  Purchase #5 $61.89   9.701%   $67.8939   $67.89   $67.90   $67.90  
  Purchase #6 $113.50   10.398%   $125.3017   $125.30   $125.30   $125.30  
  Purchase #7 $211.32   12.328%   $237.3715   $237.37   $237.35   $237.40  
  7 purchase totals = $877.50       $970.6202   $970.62   $970.65   $970.60