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 $165.93   11.399%   $184.8444   $184.84   $184.85   $184.80  
  Purchase #2 $66.69   9.618%   $73.1042   $73.10   $73.10   $73.10  
  Purchase #3 $76.54   10.279%   $84.4075   $84.41   $84.40   $84.40  
  Purchase #4 $151.72   10.313%   $167.3669   $167.37   $167.35   $167.40  
  Purchase #5 $226.52   9.605%   $248.2772   $248.28   $248.30   $248.30  
  Purchase #6 $147.88   6.470%   $157.4478   $157.45   $157.45   $157.40  
  Purchase #7 $151.50   6.537%   $161.4036   $161.40   $161.40   $161.40  
  7 purchase totals = $986.78       $1,076.8516   $1,076.85   $1,076.85   $1,076.80