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 $236.92   11.128%   $263.2845   $263.28   $263.30   $263.30  
  Purchase #2 $144.32   8.532%   $156.6334   $156.63   $156.65   $156.60  
  Purchase #3 $114.84   13.769%   $130.6523   $130.65   $130.65   $130.70  
  Purchase #4 $88.59   7.230%   $94.9951   $95.00   $95.00   $95.00  
  Purchase #5 $184.92   11.409%   $206.0175   $206.02   $206.00   $206.00  
  Purchase #6 $174.41   13.466%   $197.8961   $197.90   $197.90   $197.90  
  Purchase #7 $105.80   10.247%   $116.6413   $116.64   $116.65   $116.60  
  7 purchase totals = $1,049.80       $1,166.1202   $1,166.12   $1,166.15   $1,166.10