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 $248.63   10.866%   $275.6461   $275.65   $275.65   $275.60  
  Purchase #2 $156.73   12.841%   $176.8557   $176.86   $176.85   $176.90  
  Purchase #3 $209.33   8.716%   $227.5752   $227.58   $227.60   $227.60  
  Purchase #4 $141.87   11.420%   $158.0716   $158.07   $158.05   $158.10  
  Purchase #5 $57.29   6.633%   $61.09   $61.09   $61.10   $61.10  
  Purchase #6 $155.78   8.777%   $169.4528   $169.45   $169.45   $169.50  
  Purchase #7 $234.80   10.299%   $258.9821   $258.98   $259.00   $259.00  
  7 purchase totals = $1,204.43       $1,327.6735   $1,327.68   $1,327.70   $1,327.80