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 $228.34   11.121%   $253.7337   $253.73   $253.75   $253.70  
  Purchase #2 $45.39   4.438%   $47.4044   $47.40   $47.40   $47.40  
  Purchase #3 $207.84   4.736%   $217.6833   $217.68   $217.70   $217.70  
  Purchase #4 $125.34   5.312%   $131.9981   $132.00   $132.00   $132.00  
  Purchase #5 $222.59   11.679%   $248.5863   $248.59   $248.60   $248.60  
  Purchase #6 $77.79   6.694%   $82.9973   $83.00   $83.00   $83.00  
  Purchase #7 $48.56   3.191%   $50.1095   $50.11   $50.10   $50.10  
  7 purchase totals = $955.85       $1,032.5126   $1,032.51   $1,032.55   $1,032.50