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 $246.83   11.398%   $274.9637   $274.96   $274.95   $275.00  
  Purchase #2 $45.63   8.465%   $49.4926   $49.49   $49.50   $49.50  
  Purchase #3 $89.70   13.355%   $101.6794   $101.68   $101.70   $101.70  
  Purchase #4 $48.49   6.210%   $51.5012   $51.50   $51.50   $51.50  
  Purchase #5 $209.28   7.269%   $224.4926   $224.49   $224.50   $224.50  
  Purchase #6 $128.38   4.542%   $134.211   $134.21   $134.20   $134.20  
  Purchase #7 $53.43   13.368%   $60.5725   $60.57   $60.55   $60.60  
  7 purchase totals = $821.74       $896.9130   $896.90   $896.90   $897.00