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 $47.47   12.845%   $53.5675   $53.57   $53.55   $53.60  
  Purchase #2 $153.72   8.184%   $166.3004   $166.30   $166.30   $166.30  
  Purchase #3 $90.35   3.121%   $93.1698   $93.17   $93.15   $93.20  
  Purchase #4 $233.57   6.763%   $249.3663   $249.37   $249.35   $249.40  
  Purchase #5 $45.69   6.147%   $48.4986   $48.50   $48.50   $48.50  
  Purchase #6 $139.86   11.559%   $156.0264   $156.03   $156.05   $156.00  
  Purchase #7 $175.55   11.644%   $195.991   $195.99   $196.00   $196.00  
  7 purchase totals = $886.21       $962.9200   $962.93   $962.90   $963.00