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 $53.34   12.512%   $60.0139   $60.01   $60.00   $60.00  
  Purchase #2 $221.99   3.587%   $229.9528   $229.95   $229.95   $230.00  
  Purchase #3 $232.73   6.155%   $247.0545   $247.05   $247.05   $247.10  
  Purchase #4 $163.89   3.217%   $169.1623   $169.16   $169.15   $169.20  
  Purchase #5 $162.72   9.725%   $178.5445   $178.54   $178.55   $178.50  
  Purchase #6 $107.50   6.223%   $114.1897   $114.19   $114.20   $114.20  
  Purchase #7 $190.61   5.165%   $200.455   $200.46   $200.45   $200.50  
  7 purchase totals = $1,132.78       $1,199.3727   $1,199.36   $1,199.35   $1,199.50