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 $10.69   13.563%   $12.1399   $12.14   $12.15   $12.10  
  Purchase #2 $69.77   5.195%   $73.3946   $73.39   $73.40   $73.40  
  Purchase #3 $193.62   3.237%   $199.8875   $199.89   $199.90   $199.90  
  Purchase #4 $215.86   7.484%   $232.015   $232.02   $232.00   $232.00  
  Purchase #5 $232.28   6.535%   $247.4595   $247.46   $247.45   $247.50  
  Purchase #6 $234.48   10.374%   $258.805   $258.81   $258.80   $258.80  
  Purchase #7 $71.99   12.672%   $81.1126   $81.11   $81.10   $81.10  
  7 purchase totals = $1,028.69       $1,104.8141   $1,104.82   $1,104.80   $1,104.80