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 $47.97   13.866%   $54.6215   $54.62   $54.60   $54.60  
  Purchase #2 $187.76   13.308%   $212.7471   $212.75   $212.75   $212.70  
  Purchase #3 $245.86   13.651%   $279.4223   $279.42   $279.40   $279.40  
  Purchase #4 $207.32   8.856%   $225.6803   $225.68   $225.70   $225.70  
  Purchase #5 $126.69   5.252%   $133.3438   $133.34   $133.35   $133.30  
  Purchase #6 $113.51   3.199%   $117.1412   $117.14   $117.15   $117.10  
  Purchase #7 $214.88   11.469%   $239.5246   $239.52   $239.50   $239.50  
  7 purchase totals = $1,143.99       $1,262.4808   $1,262.47   $1,262.45   $1,262.30