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 $222.47   12.241%   $249.7026   $249.70   $249.70   $249.70  
  Purchase #2 $176.94   9.841%   $194.3527   $194.35   $194.35   $194.40  
  Purchase #3 $14.78   13.491%   $16.774   $16.77   $16.75   $16.80  
  Purchase #4 $123.95   6.601%   $132.1319   $132.13   $132.15   $132.10  
  Purchase #5 $49.44   4.176%   $51.5046   $51.50   $51.50   $51.50  
  Purchase #6 $184.30   13.782%   $209.7002   $209.70   $209.70   $209.70  
  Purchase #7 $219.28   9.257%   $239.5787   $239.58   $239.60   $239.60  
  7 purchase totals = $991.16       $1,093.7447   $1,093.73   $1,093.75   $1,093.80