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 $186.92   13.546%   $212.2402   $212.24   $212.25   $212.20  
  Purchase #2 $122.38   11.113%   $135.9801   $135.98   $136.00   $136.00  
  Purchase #3 $236.95   13.457%   $268.8364   $268.84   $268.85   $268.80  
  Purchase #4 $85.67   10.705%   $94.841   $94.84   $94.85   $94.80  
  Purchase #5 $96.60   9.345%   $105.6273   $105.63   $105.65   $105.60  
  Purchase #6 $125.80   10.870%   $139.4745   $139.47   $139.45   $139.50  
  Purchase #7 $23.35   6.396%   $24.8435   $24.84   $24.85   $24.80  
  7 purchase totals = $877.67       $981.8430   $981.84   $981.90   $981.70