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 $59.41   9.699%   $65.1722   $65.17   $65.15   $65.20  
  Purchase #2 $52.80   8.731%   $57.41   $57.41   $57.40   $57.40  
  Purchase #3 $25.26   9.568%   $27.6769   $27.68   $27.70   $27.70  
  Purchase #4 $10.27   7.344%   $11.0242   $11.02   $11.00   $11.00  
  Purchase #5 $62.95   9.738%   $69.0801   $69.08   $69.10   $69.10  
  Purchase #6 $229.66   7.825%   $247.6309   $247.63   $247.65   $247.60  
  Purchase #7 $28.54   5.505%   $30.1111   $30.11   $30.10   $30.10  
  7 purchase totals = $468.89       $508.1054   $508.10   $508.10   $508.10