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 $121.63   4.794%   $127.4609   $127.46   $127.45   $127.50  
  Purchase #2 $42.85   6.182%   $45.499   $45.50   $45.50   $45.50  
  Purchase #3 $62.29   12.300%   $69.9517   $69.95   $69.95   $70.00  
  Purchase #4 $113.34   9.649%   $124.2762   $124.28   $124.30   $124.30  
  Purchase #5 $196.27   10.609%   $217.0923   $217.09   $217.10   $217.10  
  Purchase #6 $132.29   3.580%   $137.026   $137.03   $137.05   $137.00  
  Purchase #7 $210.87   9.722%   $231.3708   $231.37   $231.35   $231.40  
  7 purchase totals = $879.54       $952.6769   $952.68   $952.70   $952.80