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 $226.83   11.765%   $253.5165   $253.52   $253.50   $253.50  
  Purchase #2 $144.95   11.124%   $161.0742   $161.07   $161.05   $161.10  
  Purchase #3 $117.83   9.788%   $129.3632   $129.36   $129.35   $129.40  
  Purchase #4 $213.37   6.674%   $227.6103   $227.61   $227.60   $227.60  
  Purchase #5 $179.62   6.567%   $191.4156   $191.42   $191.40   $191.40  
  Purchase #6 $194.59   11.653%   $217.2656   $217.27   $217.25   $217.30  
  Purchase #7 $236.42   11.632%   $263.9204   $263.92   $263.90   $263.90  
  7 purchase totals = $1,313.61       $1,444.1658   $1,444.17   $1,444.05   $1,444.20