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 $164.68   11.321%   $183.3234   $183.32   $183.30   $183.30  
  Purchase #2 $157.52   12.306%   $176.9044   $176.90   $176.90   $176.90  
  Purchase #3 $106.45   7.865%   $114.8223   $114.82   $114.80   $114.80  
  Purchase #4 $46.58   9.113%   $50.8248   $50.82   $50.80   $50.80  
  Purchase #5 $19.38   10.734%   $21.4602   $21.46   $21.45   $21.50  
  Purchase #6 $147.51   10.197%   $162.5516   $162.55   $162.55   $162.60  
  Purchase #7 $167.53   9.645%   $183.6883   $183.69   $183.70   $183.70  
  7 purchase totals = $809.65       $893.5750   $893.56   $893.50   $893.60