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 $64.43   3.397%   $66.6187   $66.62   $66.60   $66.60  
  Purchase #2 $225.74   13.689%   $256.6415   $256.64   $256.65   $256.60  
  Purchase #3 $51.66   6.220%   $54.8733   $54.87   $54.85   $54.90  
  Purchase #4 $238.98   3.866%   $248.219   $248.22   $248.20   $248.20  
  Purchase #5 $214.49   5.455%   $226.1904   $226.19   $226.20   $226.20  
  Purchase #6 $69.59   13.634%   $79.0779   $79.08   $79.10   $79.10  
  Purchase #7 $109.42   8.103%   $118.2863   $118.29   $118.30   $118.30  
  7 purchase totals = $974.31       $1,049.9071   $1,049.91   $1,049.90   $1,049.90