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 $112.65   6.306%   $119.7537   $119.75   $119.75   $119.80  
  Purchase #2 $89.54   11.301%   $99.6589   $99.66   $99.65   $99.70  
  Purchase #3 $190.29   3.543%   $197.032   $197.03   $197.05   $197.00  
  Purchase #4 $175.73   12.109%   $197.0091   $197.01   $197.00   $197.00  
  Purchase #5 $23.71   6.494%   $25.2497   $25.25   $25.25   $25.20  
  Purchase #6 $208.47   8.124%   $225.4061   $225.41   $225.40   $225.40  
  Purchase #7 $105.62   11.732%   $118.0113   $118.01   $118.00   $118.00  
  7 purchase totals = $906.01       $982.1208   $982.12   $982.10   $982.10