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 $90.71   4.760%   $95.0278   $95.03   $95.05   $95.00  
  Purchase #2 $196.49   8.387%   $212.9696   $212.97   $212.95   $213.00  
  Purchase #3 $50.74   4.222%   $52.8822   $52.88   $52.90   $52.90  
  Purchase #4 $162.49   9.522%   $177.9623   $177.96   $177.95   $178.00  
  Purchase #5 $87.72   11.731%   $98.0104   $98.01   $98.00   $98.00  
  Purchase #6 $119.78   13.582%   $136.0485   $136.05   $136.05   $136.00  
  Purchase #7 $134.78   3.433%   $139.407   $139.41   $139.40   $139.40  
  7 purchase totals = $842.71       $912.3078   $912.31   $912.30   $912.30