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 $65.84   5.763%   $69.6344   $69.63   $69.65   $69.60  
  Purchase #2 $242.74   5.762%   $256.7267   $256.73   $256.75   $256.70  
  Purchase #3 $141.59   13.361%   $160.5078   $160.51   $160.50   $160.50  
  Purchase #4 $57.96   13.640%   $65.8657   $65.87   $65.85   $65.90  
  Purchase #5 $234.95   6.309%   $249.773   $249.77   $249.75   $249.80  
  Purchase #6 $185.71   12.544%   $209.0055   $209.01   $209.00   $209.00  
  Purchase #7 $172.36   12.287%   $193.5379   $193.54   $193.55   $193.50  
  7 purchase totals = $1,101.15       $1,205.0510   $1,205.06   $1,205.05   $1,205.00