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 $64.44   11.716%   $71.9898   $71.99   $72.00   $72.00  
  Purchase #2 $115.91   8.581%   $125.8562   $125.86   $125.85   $125.90  
  Purchase #3 $172.86   12.441%   $194.3655   $194.37   $194.35   $194.40  
  Purchase #4 $214.30   3.816%   $222.4777   $222.48   $222.50   $222.50  
  Purchase #5 $247.99   10.478%   $273.9744   $273.97   $273.95   $274.00  
  Purchase #6 $119.68   5.417%   $126.1631   $126.16   $126.15   $126.20  
  Purchase #7 $63.36   10.320%   $69.8988   $69.90   $69.90   $69.90  
  7 purchase totals = $998.54       $1,084.7255   $1,084.73   $1,084.70   $1,084.90