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 $241.87   3.210%   $249.634   $249.63   $249.65   $249.60  
  Purchase #2 $179.47   6.172%   $190.5469   $190.55   $190.55   $190.50  
  Purchase #3 $143.36   7.394%   $153.96   $153.96   $153.95   $154.00  
  Purchase #4 $114.64   11.375%   $127.6803   $127.68   $127.70   $127.70  
  Purchase #5 $206.60   10.742%   $228.793   $228.79   $228.80   $228.80  
  Purchase #6 $141.90   7.685%   $152.805   $152.81   $152.80   $152.80  
  Purchase #7 $119.96   8.370%   $130.0007   $130.00   $130.00   $130.00  
  7 purchase totals = $1,147.80       $1,233.4199   $1,233.42   $1,233.45   $1,233.40