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 $224.97   10.687%   $249.0125   $249.01   $249.00   $249.00  
  Purchase #2 $104.53   13.357%   $118.4921   $118.49   $118.50   $118.50  
  Purchase #3 $176.84   6.472%   $188.2851   $188.29   $188.30   $188.30  
  Purchase #4 $181.26   7.506%   $194.8654   $194.87   $194.85   $194.90  
  Purchase #5 $175.84   11.284%   $195.6818   $195.68   $195.70   $195.70  
  Purchase #6 $75.58   12.659%   $85.1477   $85.15   $85.15   $85.10  
  Purchase #7 $37.62   7.565%   $40.466   $40.47   $40.45   $40.50  
  7 purchase totals = $976.64       $1,071.9506   $1,071.96   $1,071.95   $1,072.00