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	$246.29	10.872%	$273.0666	$273.07	$273.05	$273.10
Purchase #2	$31.62	6.792%	$33.7676	$33.77	$33.75	$33.80
Purchase #3	$23.49	12.313%	$26.3823	$26.38	$26.40	$26.40
Purchase #4	$175.94	5.323%	$185.3053	$185.31	$185.30	$185.30
Purchase #5	$67.80	6.749%	$72.3758	$72.38	$72.40	$72.40
Purchase #6	$226.93	13.291%	$257.0913	$257.09	$257.10	$257.10
Purchase #7	$37.30	9.620%	$40.8883	$40.89	$40.90	$40.90
7 purchase totals =	$809.37		$888.8772	$888.89	$888.90	$889.00