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 $244.89   9.162%   $267.3268   $267.33   $267.35   $267.30  
  Purchase #2 $186.79   6.838%   $199.5627   $199.56   $199.55   $199.60  
  Purchase #3 $15.91   4.204%   $16.5789   $16.58   $16.60   $16.60  
  Purchase #4 $96.57   7.479%   $103.7925   $103.79   $103.80   $103.80  
  Purchase #5 $173.26   13.517%   $196.6796   $196.68   $196.70   $196.70  
  Purchase #6 $63.54   13.777%   $72.2939   $72.29   $72.30   $72.30  
  Purchase #7 $192.97   10.459%   $213.1527   $213.15   $213.15   $213.20  
  7 purchase totals = $973.93       $1,069.3871   $1,069.38   $1,069.45   $1,069.50