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 $246.99   11.569%   $275.5643   $275.56   $275.55   $275.60  
  Purchase #2 $213.96   9.292%   $233.8412   $233.84   $233.85   $233.80  
  Purchase #3 $156.58   12.863%   $176.7209   $176.72   $176.70   $176.70  
  Purchase #4 $135.26   4.608%   $141.4928   $141.49   $141.50   $141.50  
  Purchase #5 $225.51   5.124%   $237.0651   $237.07   $237.05   $237.10  
  Purchase #6 $151.29   4.792%   $158.5398   $158.54   $158.55   $158.50  
  Purchase #7 $184.33   8.124%   $199.305   $199.31   $199.30   $199.30  
  7 purchase totals = $1,313.92       $1,422.5291   $1,422.53   $1,422.50   $1,422.50