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 $87.54   9.832%   $96.1469   $96.15   $96.15   $96.10  
  Purchase #2 $86.30   11.204%   $95.9691   $95.97   $95.95   $96.00  
  Purchase #3 $41.91   4.494%   $43.7934   $43.79   $43.80   $43.80  
  Purchase #4 $104.62   9.752%   $114.8225   $114.82   $114.80   $114.80  
  Purchase #5 $41.75   4.367%   $43.5732   $43.57   $43.55   $43.60  
  Purchase #6 $56.45   6.350%   $60.0346   $60.03   $60.05   $60.00  
  Purchase #7 $129.99   3.868%   $135.018   $135.02   $135.00   $135.00  
  7 purchase totals = $548.56       $589.3577   $589.35   $589.30   $589.30