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 $245.70   9.398%   $268.7909   $268.79   $268.80   $268.80  
  Purchase #2 $127.38   11.372%   $141.8657   $141.87   $141.85   $141.90  
  Purchase #3 $155.84   7.873%   $168.1093   $168.11   $168.10   $168.10  
  Purchase #4 $199.26   4.616%   $208.4578   $208.46   $208.45   $208.50  
  Purchase #5 $161.70   7.574%   $173.9472   $173.95   $173.95   $173.90  
  Purchase #6 $222.51   12.489%   $250.2993   $250.30   $250.30   $250.30  
  Purchase #7 $231.69   3.803%   $240.5012   $240.50   $240.50   $240.50  
  7 purchase totals = $1,344.08       $1,451.9714   $1,451.98   $1,451.95   $1,452.00