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 $87.93   11.726%   $98.2407   $98.24   $98.25   $98.20  
  Purchase #2 $225.39   11.526%   $251.3685   $251.37   $251.35   $251.40  
  Purchase #3 $121.62   7.741%   $131.0346   $131.03   $131.05   $131.00  
  Purchase #4 $178.61   10.316%   $197.0354   $197.04   $197.05   $197.00  
  Purchase #5 $215.37   4.586%   $225.2469   $225.25   $225.25   $225.20  
  Purchase #6 $14.66   4.499%   $15.3196   $15.32   $15.30   $15.30  
  Purchase #7 $73.50   10.768%   $81.4145   $81.41   $81.40   $81.40  
  7 purchase totals = $917.08       $999.6602   $999.66   $999.65   $999.50