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 $221.90   13.568%   $252.0074   $252.01   $252.00   $252.00  
  Purchase #2 $114.36   9.282%   $124.9749   $124.97   $124.95   $125.00  
  Purchase #3 $230.84   8.491%   $250.4406   $250.44   $250.45   $250.40  
  Purchase #4 $9.71   11.569%   $10.8333   $10.83   $10.85   $10.80  
  Purchase #5 $26.90   11.333%   $29.9486   $29.95   $29.95   $29.90  
  Purchase #6 $232.44   12.668%   $261.8855   $261.89   $261.90   $261.90  
  Purchase #7 $190.35   6.112%   $201.9842   $201.98   $202.00   $202.00  
  7 purchase totals = $1,026.50       $1,132.0745   $1,132.07   $1,132.10   $1,132.00