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 $81.43   8.727%   $88.5364   $88.54   $88.55   $88.50  
  Purchase #2 $222.91   10.643%   $246.6343   $246.63   $246.65   $246.60  
  Purchase #3 $235.74   7.177%   $252.6591   $252.66   $252.65   $252.70  
  Purchase #4 $183.67   7.605%   $197.6381   $197.64   $197.65   $197.60  
  Purchase #5 $33.53   3.248%   $34.6191   $34.62   $34.60   $34.60  
  Purchase #6 $208.82   8.598%   $226.7743   $226.77   $226.75   $226.80  
  Purchase #7 $209.70   3.182%   $216.3727   $216.37   $216.35   $216.40  
  7 purchase totals = $1,175.80       $1,263.2340   $1,263.23   $1,263.20   $1,263.20