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 $83.77   13.292%   $94.9047   $94.90   $94.90   $94.90  
  Purchase #2 $166.51   10.567%   $184.1051   $184.11   $184.10   $184.10  
  Purchase #3 $112.81   3.591%   $116.861   $116.86   $116.85   $116.90  
  Purchase #4 $103.74   10.125%   $114.2437   $114.24   $114.25   $114.20  
  Purchase #5 $41.28   11.724%   $46.1197   $46.12   $46.10   $46.10  
  Purchase #6 $201.84   13.510%   $229.1086   $229.11   $229.10   $229.10  
  Purchase #7 $52.95   5.257%   $55.7336   $55.73   $55.75   $55.70  
  7 purchase totals = $762.90       $841.0764   $841.07   $841.05   $841.00