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 $218.65   6.568%   $233.0109   $233.01   $233.00   $233.00  
  Purchase #2 $59.86   7.626%   $64.4249   $64.42   $64.40   $64.40  
  Purchase #3 $32.36   9.717%   $35.5044   $35.50   $35.50   $35.50  
  Purchase #4 $98.57   5.448%   $103.9401   $103.94   $103.95   $103.90  
  Purchase #5 $219.87   6.259%   $233.6317   $233.63   $233.65   $233.60  
  Purchase #6 $6.82   13.428%   $7.7358   $7.74   $7.75   $7.70  
  Purchase #7 $192.46   7.600%   $207.087   $207.09   $207.10   $207.10  
  7 purchase totals = $828.59       $885.3348   $885.33   $885.35   $885.20