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 $75.29   12.692%   $84.8458   $84.85   $84.85   $84.80  
  Purchase #2 $83.45   12.531%   $93.9071   $93.91   $93.90   $93.90  
  Purchase #3 $176.77   9.511%   $193.5826   $193.58   $193.60   $193.60  
  Purchase #4 $115.95   13.296%   $131.3667   $131.37   $131.35   $131.40  
  Purchase #5 $176.27   6.649%   $187.9902   $187.99   $188.00   $188.00  
  Purchase #6 $238.40   9.555%   $261.1791   $261.18   $261.20   $261.20  
  Purchase #7 $54.38   5.222%   $57.2197   $57.22   $57.20   $57.20  
  7 purchase totals = $920.51       $1,010.0912   $1,010.10   $1,010.10   $1,010.10