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 $199.95   3.324%   $206.5963   $206.60   $206.60   $206.60  
  Purchase #2 $34.52   11.873%   $38.6186   $38.62   $38.60   $38.60  
  Purchase #3 $96.50   6.689%   $102.9549   $102.95   $102.95   $103.00  
  Purchase #4 $174.87   11.612%   $195.1759   $195.18   $195.20   $195.20  
  Purchase #5 $201.83   7.644%   $217.2579   $217.26   $217.25   $217.30  
  Purchase #6 $16.41   9.714%   $18.0041   $18.00   $18.00   $18.00  
  Purchase #7 $65.32   10.335%   $72.0708   $72.07   $72.05   $72.10  
  7 purchase totals = $789.40       $850.6785   $850.68   $850.65   $850.80