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 $226.63   10.635%   $250.7321   $250.73   $250.75   $250.70  
  Purchase #2 $227.43   3.534%   $235.4674   $235.47   $235.45   $235.50  
  Purchase #3 $125.53   13.789%   $142.8393   $142.84   $142.85   $142.80  
  Purchase #4 $33.75   3.634%   $34.9765   $34.98   $35.00   $35.00  
  Purchase #5 $117.35   6.779%   $125.3052   $125.31   $125.30   $125.30  
  Purchase #6 $59.89   11.334%   $66.6779   $66.68   $66.70   $66.70  
  Purchase #7 $176.99   12.853%   $199.7385   $199.74   $199.75   $199.70  
  7 purchase totals = $967.57       $1,055.7369   $1,055.75   $1,055.80   $1,055.70