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 $101.29   12.559%   $114.011   $114.01   $114.00   $114.00  
  Purchase #2 $61.82   5.391%   $65.1527   $65.15   $65.15   $65.20  
  Purchase #3 $83.92   8.824%   $91.3251   $91.33   $91.35   $91.30  
  Purchase #4 $119.47   7.396%   $128.306   $128.31   $128.30   $128.30  
  Purchase #5 $194.92   8.725%   $211.9268   $211.93   $211.95   $211.90  
  Purchase #6 $134.32   7.537%   $144.4437   $144.44   $144.45   $144.40  
  Purchase #7 $66.82   10.657%   $73.941   $73.94   $73.95   $73.90  
  7 purchase totals = $762.56       $829.1063   $829.11   $829.15   $829.00