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 $83.46   11.384%   $92.9611   $92.96   $92.95   $93.00  
  Purchase #2 $201.52   9.679%   $221.0251   $221.03   $221.05   $221.00  
  Purchase #3 $20.72   12.175%   $23.2427   $23.24   $23.25   $23.20  
  Purchase #4 $80.71   4.726%   $84.5244   $84.52   $84.50   $84.50  
  Purchase #5 $182.67   11.806%   $204.236   $204.24   $204.25   $204.20  
  Purchase #6 $89.36   5.247%   $94.0487   $94.05   $94.05   $94.00  
  Purchase #7 $128.34   6.426%   $136.5871   $136.59   $136.60   $136.60  
  7 purchase totals = $786.78       $856.6251   $856.63   $856.65   $856.50