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 $245.50   8.748%   $266.9763   $266.98   $267.00   $267.00  
  Purchase #2 $102.31   12.370%   $114.9657   $114.97   $114.95   $115.00  
  Purchase #3 $167.41   9.142%   $182.7146   $182.71   $182.70   $182.70  
  Purchase #4 $171.54   3.151%   $176.9452   $176.95   $176.95   $176.90  
  Purchase #5 $196.64   6.657%   $209.7303   $209.73   $209.75   $209.70  
  Purchase #6 $187.78   12.472%   $211.1999   $211.20   $211.20   $211.20  
  Purchase #7 $58.94   9.222%   $64.3754   $64.38   $64.40   $64.40  
  7 purchase totals = $1,130.12       $1,226.9074   $1,226.92   $1,226.95   $1,226.90