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 $111.40   6.283%   $118.3993   $118.40   $118.40   $118.40  
  Purchase #2 $225.53   12.401%   $253.498   $253.50   $253.50   $253.50  
  Purchase #3 $44.45   5.512%   $46.9001   $46.90   $46.90   $46.90  
  Purchase #4 $187.59   8.172%   $202.9199   $202.92   $202.90   $202.90  
  Purchase #5 $136.65   11.197%   $151.9507   $151.95   $151.95   $152.00  
  Purchase #6 $152.85   6.853%   $163.3248   $163.32   $163.30   $163.30  
  Purchase #7 $69.25   4.334%   $72.2513   $72.25   $72.25   $72.30  
  7 purchase totals = $927.72       $1,009.2441   $1,009.24   $1,009.20   $1,009.30