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 $47.61   6.268%   $50.5942   $50.59   $50.60   $50.60  
  Purchase #2 $226.64   9.708%   $248.6422   $248.64   $248.65   $248.60  
  Purchase #3 $76.60   11.226%   $85.1991   $85.20   $85.20   $85.20  
  Purchase #4 $132.39   10.305%   $146.0328   $146.03   $146.05   $146.00  
  Purchase #5 $97.49   4.713%   $102.0847   $102.08   $102.10   $102.10  
  Purchase #6 $166.61   12.778%   $187.8994   $187.90   $187.90   $187.90  
  Purchase #7 $152.50   13.186%   $172.6087   $172.61   $172.60   $172.60  
  7 purchase totals = $899.84       $993.0611   $993.05   $993.10   $993.00