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 $22.91   9.778%   $25.1501   $25.15   $25.15   $25.20  
  Purchase #2 $55.32   12.450%   $62.2073   $62.21   $62.20   $62.20  
  Purchase #3 $179.95   8.770%   $195.7316   $195.73   $195.75   $195.70  
  Purchase #4 $103.80   12.728%   $117.0117   $117.01   $117.00   $117.00  
  Purchase #5 $49.37   10.195%   $54.4033   $54.40   $54.40   $54.40  
  Purchase #6 $110.69   7.497%   $118.9884   $118.99   $119.00   $119.00  
  Purchase #7 $144.71   9.541%   $158.5168   $158.52   $158.50   $158.50  
  7 purchase totals = $666.75       $732.0092   $732.01   $732.00   $732.00