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 $215.51   12.295%   $242.007   $242.01   $242.00   $242.00  
  Purchase #2 $181.33   10.172%   $199.7749   $199.77   $199.75   $199.80  
  Purchase #3 $247.82   7.809%   $267.1723   $267.17   $267.15   $267.20  
  Purchase #4 $140.51   4.141%   $146.3285   $146.33   $146.35   $146.30  
  Purchase #5 $218.44   10.448%   $241.2626   $241.26   $241.25   $241.30  
  Purchase #6 $76.58   6.166%   $81.3019   $81.30   $81.30   $81.30  
  Purchase #7 $240.75   11.424%   $268.2533   $268.25   $268.25   $268.30  
  7 purchase totals = $1,320.94       $1,446.1005   $1,446.09   $1,446.05   $1,446.20