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 $10.35   13.368%   $11.7336   $11.73   $11.75   $11.70  
  Purchase #2 $96.82   11.210%   $107.6735   $107.67   $107.65   $107.70  
  Purchase #3 $183.63   13.357%   $208.1575   $208.16   $208.15   $208.20  
  Purchase #4 $92.92   13.716%   $105.6649   $105.66   $105.65   $105.70  
  Purchase #5 $229.64   6.734%   $245.104   $245.10   $245.10   $245.10  
  Purchase #6 $207.67   5.643%   $219.3888   $219.39   $219.40   $219.40  
  Purchase #7 $14.38   11.367%   $16.0146   $16.01   $16.00   $16.00  
  7 purchase totals = $835.41       $913.7369   $913.72   $913.70   $913.80