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 $232.45   13.261%   $263.2752   $263.28   $263.30   $263.30  
  Purchase #2 $69.27   9.223%   $75.6588   $75.66   $75.65   $75.70  
  Purchase #3 $182.73   9.306%   $199.7349   $199.73   $199.75   $199.70  
  Purchase #4 $146.74   3.548%   $151.9463   $151.95   $151.95   $151.90  
  Purchase #5 $246.76   6.716%   $263.3324   $263.33   $263.35   $263.30  
  Purchase #6 $52.56   7.833%   $56.677   $56.68   $56.70   $56.70  
  Purchase #7 $229.68   8.744%   $249.7632   $249.76   $249.75   $249.80  
  7 purchase totals = $1,160.19       $1,260.3878   $1,260.39   $1,260.45   $1,260.40