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 $88.93   5.320%   $93.6611   $93.66   $93.65   $93.70  
  Purchase #2 $29.56   13.504%   $33.5518   $33.55   $33.55   $33.60  
  Purchase #3 $197.44   5.771%   $208.8343   $208.83   $208.85   $208.80  
  Purchase #4 $47.50   3.185%   $49.0129   $49.01   $49.00   $49.00  
  Purchase #5 $101.31   3.802%   $105.1618   $105.16   $105.15   $105.20  
  Purchase #6 $243.67   10.406%   $269.0263   $269.03   $269.05   $269.00  
  Purchase #7 $213.63   5.466%   $225.307   $225.31   $225.30   $225.30  
  7 purchase totals = $922.04       $984.5552   $984.55   $984.55   $984.60