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 $197.56   13.752%   $224.7285   $224.73   $224.75   $224.70  
  Purchase #2 $168.64   8.521%   $183.0098   $183.01   $183.00   $183.00  
  Purchase #3 $169.80   6.149%   $180.241   $180.24   $180.25   $180.20  
  Purchase #4 $46.89   8.614%   $50.9291   $50.93   $50.95   $50.90  
  Purchase #5 $75.86   10.279%   $83.6576   $83.66   $83.65   $83.70  
  Purchase #6 $197.34   13.819%   $224.6104   $224.61   $224.60   $224.60  
  Purchase #7 $208.71   6.743%   $222.7833   $222.78   $222.80   $222.80  
  7 purchase totals = $1,064.80       $1,169.9597   $1,169.96   $1,170.00   $1,169.90