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 $238.58   7.284%   $255.9582   $255.96   $255.95   $256.00  
  Purchase #2 $83.48   12.549%   $93.9559   $93.96   $93.95   $94.00  
  Purchase #3 $239.53   11.154%   $266.2472   $266.25   $266.25   $266.20  
  Purchase #4 $53.87   12.111%   $60.3942   $60.39   $60.40   $60.40  
  Purchase #5 $216.53   9.781%   $237.7088   $237.71   $237.70   $237.70  
  Purchase #6 $233.66   3.471%   $241.7703   $241.77   $241.75   $241.80  
  Purchase #7 $63.63   10.759%   $70.476   $70.48   $70.50   $70.50  
  7 purchase totals = $1,129.28       $1,226.5106   $1,226.52   $1,226.50   $1,226.60