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 $223.58   6.708%   $238.5777   $238.58   $238.60   $238.60  
  Purchase #2 $106.87   11.639%   $119.3086   $119.31   $119.30   $119.30  
  Purchase #3 $224.26   11.134%   $249.2291   $249.23   $249.25   $249.20  
  Purchase #4 $135.41   7.675%   $145.8027   $145.80   $145.80   $145.80  
  Purchase #5 $98.45   9.639%   $107.9396   $107.94   $107.95   $107.90  
  Purchase #6 $112.46   3.727%   $116.6514   $116.65   $116.65   $116.70  
  Purchase #7 $60.57   11.199%   $67.3532   $67.35   $67.35   $67.40  
  7 purchase totals = $961.60       $1,044.8623   $1,044.86   $1,044.90   $1,044.90