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 $236.32   7.489%   $254.018   $254.02   $254.00   $254.00  
  Purchase #2 $204.65   6.162%   $217.2605   $217.26   $217.25   $217.30  
  Purchase #3 $151.84   11.590%   $169.4383   $169.44   $169.45   $169.40  
  Purchase #4 $46.93   5.459%   $49.4919   $49.49   $49.50   $49.50  
  Purchase #5 $190.76   11.694%   $213.0675   $213.07   $213.05   $213.10  
  Purchase #6 $160.99   11.465%   $179.4475   $179.45   $179.45   $179.40  
  Purchase #7 $115.72   9.636%   $126.8708   $126.87   $126.85   $126.90  
  7 purchase totals = $1,107.21       $1,209.5945   $1,209.60   $1,209.55   $1,209.60