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 $225.51   10.412%   $248.9901   $248.99   $249.00   $249.00  
  Purchase #2 $23.57   4.723%   $24.6832   $24.68   $24.70   $24.70  
  Purchase #3 $108.30   4.857%   $113.5601   $113.56   $113.55   $113.60  
  Purchase #4 $85.99   10.475%   $94.9975   $95.00   $95.00   $95.00  
  Purchase #5 $149.73   4.743%   $156.8317   $156.83   $156.85   $156.80  
  Purchase #6 $83.98   3.180%   $86.6506   $86.65   $86.65   $86.70  
  Purchase #7 $213.69   5.219%   $224.8425   $224.84   $224.85   $224.80  
  7 purchase totals = $890.77       $950.5557   $950.55   $950.60   $950.60