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 $171.74   6.344%   $182.6352   $182.64   $182.65   $182.60  
  Purchase #2 $33.43   4.414%   $34.9056   $34.91   $34.90   $34.90  
  Purchase #3 $176.94   4.223%   $184.4122   $184.41   $184.40   $184.40  
  Purchase #4 $206.94   13.450%   $234.7734   $234.77   $234.75   $234.80  
  Purchase #5 $152.42   11.346%   $169.7136   $169.71   $169.70   $169.70  
  Purchase #6 $196.58   3.399%   $203.2618   $203.26   $203.25   $203.30  
  Purchase #7 $32.65   5.636%   $34.4902   $34.49   $34.50   $34.50  
  7 purchase totals = $970.70       $1,044.1920   $1,044.19   $1,044.15   $1,044.20