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 $52.98   9.823%   $58.1842   $58.18   $58.20   $58.20  
  Purchase #2 $76.48   6.846%   $81.7158   $81.72   $81.70   $81.70  
  Purchase #3 $28.75   6.806%   $30.7067   $30.71   $30.70   $30.70  
  Purchase #4 $186.68   8.182%   $201.9542   $201.95   $201.95   $202.00  
  Purchase #5 $68.60   7.152%   $73.5063   $73.51   $73.50   $73.50  
  Purchase #6 $211.90   10.701%   $234.5754   $234.58   $234.60   $234.60  
  Purchase #7 $51.41   8.330%   $55.6925   $55.69   $55.70   $55.70  
  7 purchase totals = $676.80       $736.3351   $736.34   $736.35   $736.40