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 $186.77   4.739%   $195.621   $195.62   $195.60   $195.60  
  Purchase #2 $32.86   10.363%   $36.2653   $36.27   $36.25   $36.30  
  Purchase #3 $88.59   11.629%   $98.8921   $98.89   $98.90   $98.90  
  Purchase #4 $31.30   11.459%   $34.8867   $34.89   $34.90   $34.90  
  Purchase #5 $174.97   13.867%   $199.2331   $199.23   $199.25   $199.20  
  Purchase #6 $195.76   9.504%   $214.365   $214.37   $214.35   $214.40  
  Purchase #7 $60.86   7.616%   $65.4951   $65.50   $65.50   $65.50  
  7 purchase totals = $771.11       $844.7583   $844.77   $844.75   $844.80