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 $208.29   12.366%   $234.0471   $234.05   $234.05   $234.00  
  Purchase #2 $8.37   4.407%   $8.7389   $8.74   $8.75   $8.70  
  Purchase #3 $196.67   10.330%   $216.986   $216.99   $217.00   $217.00  
  Purchase #4 $113.41   5.105%   $119.1996   $119.20   $119.20   $119.20  
  Purchase #5 $238.85   4.170%   $248.81   $248.81   $248.80   $248.80  
  Purchase #6 $99.53   7.731%   $107.2247   $107.22   $107.20   $107.20  
  Purchase #7 $120.72   9.810%   $132.5626   $132.56   $132.55   $132.60  
  7 purchase totals = $985.84       $1,067.5689   $1,067.57   $1,067.55   $1,067.50