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	$65.33	13.110%	$73.8948	$73.89	$73.90	$73.90
Purchase #2	$202.38	4.124%	$210.7262	$210.73	$210.75	$210.70
Purchase #3	$57.83	12.417%	$65.0108	$65.01	$65.00	$65.00
Purchase #4	$133.41	13.467%	$151.3763	$151.38	$151.40	$151.40
Purchase #5	$48.80	9.680%	$53.5238	$53.52	$53.50	$53.50
Purchase #6	$72.60	3.194%	$74.9188	$74.92	$74.90	$74.90
Purchase #7	$191.47	4.178%	$199.4696	$199.47	$199.45	$199.50
7 purchase totals =	$771.82		$828.9203	$828.92	$828.90	$828.90