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 $245.34   12.183%   $275.2298   $275.23   $275.25   $275.20  
  Purchase #2 $28.57   9.165%   $31.1884   $31.19   $31.20   $31.20  
  Purchase #3 $176.88   10.504%   $195.4595   $195.46   $195.45   $195.50  
  Purchase #4 $193.65   7.543%   $208.257   $208.26   $208.25   $208.30  
  Purchase #5 $234.97   12.217%   $263.6763   $263.68   $263.70   $263.70  
  Purchase #6 $103.42   7.754%   $111.4392   $111.44   $111.45   $111.40  
  Purchase #7 $67.60   11.398%   $75.305   $75.31   $75.30   $75.30  
  7 purchase totals = $1,050.43       $1,160.5552   $1,160.57   $1,160.60   $1,160.60