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 $52.31   13.299%   $59.2667   $59.27   $59.25   $59.30  
  Purchase #2 $171.81   7.550%   $184.7817   $184.78   $184.80   $184.80  
  Purchase #3 $83.88   5.796%   $88.7417   $88.74   $88.75   $88.70  
  Purchase #4 $207.87   9.451%   $227.5158   $227.52   $227.50   $227.50  
  Purchase #5 $34.42   9.409%   $37.6586   $37.66   $37.65   $37.70  
  Purchase #6 $172.49   8.563%   $187.2603   $187.26   $187.25   $187.30  
  Purchase #7 $91.73   5.716%   $96.9733   $96.97   $96.95   $97.00  
  7 purchase totals = $814.51       $882.1981   $882.20   $882.15   $882.30