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 $214.89   6.852%   $229.6143   $229.61   $229.60   $229.60  
  Purchase #2 $98.34   3.417%   $101.7003   $101.70   $101.70   $101.70  
  Purchase #3 $9.72   8.451%   $10.5414   $10.54   $10.55   $10.50  
  Purchase #4 $121.48   4.110%   $126.4728   $126.47   $126.45   $126.50  
  Purchase #5 $206.75   6.828%   $220.8669   $220.87   $220.85   $220.90  
  Purchase #6 $18.86   7.558%   $20.2854   $20.29   $20.30   $20.30  
  Purchase #7 $201.53   5.508%   $212.6303   $212.63   $212.65   $212.60  
  7 purchase totals = $871.57       $922.1114   $922.11   $922.10   $922.10