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 $59.99   8.390%   $65.0232   $65.02   $65.00   $65.00  
  Purchase #2 $129.75   13.796%   $147.6503   $147.65   $147.65   $147.70  
  Purchase #3 $185.82   7.335%   $199.4499   $199.45   $199.45   $199.40  
  Purchase #4 $195.34   9.528%   $213.952   $213.95   $213.95   $214.00  
  Purchase #5 $148.38   11.421%   $165.3265   $165.33   $165.35   $165.30  
  Purchase #6 $174.62   9.146%   $190.5907   $190.59   $190.60   $190.60  
  Purchase #7 $207.39   4.755%   $217.2514   $217.25   $217.25   $217.30  
  7 purchase totals = $1,101.29       $1,199.2440   $1,199.24   $1,199.25   $1,199.30