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 $34.31   4.844%   $35.972   $35.97   $35.95   $36.00  
  Purchase #2 $65.26   3.671%   $67.6557   $67.66   $67.65   $67.70  
  Purchase #3 $43.63   6.319%   $46.387   $46.39   $46.40   $46.40  
  Purchase #4 $39.46   8.113%   $42.6614   $42.66   $42.65   $42.70  
  Purchase #5 $245.97   7.428%   $264.2407   $264.24   $264.25   $264.20  
  Purchase #6 $124.25   12.296%   $139.5278   $139.53   $139.55   $139.50  
  Purchase #7 $60.45   3.822%   $62.7604   $62.76   $62.75   $62.80  
  7 purchase totals = $613.33       $659.2050   $659.21   $659.20   $659.30