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 $212.55   13.666%   $241.5971   $241.60   $241.60   $241.60  
  Purchase #2 $107.97   10.271%   $119.0596   $119.06   $119.05   $119.10  
  Purchase #3 $101.27   5.281%   $106.6181   $106.62   $106.60   $106.60  
  Purchase #4 $224.73   4.397%   $234.6114   $234.61   $234.60   $234.60  
  Purchase #5 $117.25   11.234%   $130.4219   $130.42   $130.40   $130.40  
  Purchase #6 $157.84   7.196%   $169.1982   $169.20   $169.20   $169.20  
  Purchase #7 $218.58   13.615%   $248.3397   $248.34   $248.35   $248.30  
  7 purchase totals = $1,140.19       $1,249.8460   $1,249.85   $1,249.80   $1,249.80