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 $234.87   11.769%   $262.5119   $262.51   $262.50   $262.50  
  Purchase #2 $233.56   7.622%   $251.3619   $251.36   $251.35   $251.40  
  Purchase #3 $65.54   11.191%   $72.8746   $72.87   $72.85   $72.90  
  Purchase #4 $183.47   5.343%   $193.2728   $193.27   $193.25   $193.30  
  Purchase #5 $92.72   6.743%   $98.9721   $98.97   $98.95   $99.00  
  Purchase #6 $212.97   8.198%   $230.4293   $230.43   $230.45   $230.40  
  Purchase #7 $107.40   11.516%   $119.7682   $119.77   $119.75   $119.80  
  7 purchase totals = $1,130.53       $1,229.1908   $1,229.18   $1,229.10   $1,229.30