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	$219.54	12.504%	$246.9913	$246.99	$247.00	$247.00
Purchase #2	$106.47	4.502%	$111.2633	$111.26	$111.25	$111.30
Purchase #3	$90.64	9.694%	$99.4266	$99.43	$99.45	$99.40
Purchase #4	$72.38	10.672%	$80.1044	$80.10	$80.10	$80.10
Purchase #5	$73.81	6.568%	$78.6578	$78.66	$78.65	$78.70
Purchase #6	$74.57	12.546%	$83.9256	$83.93	$83.95	$83.90
Purchase #7	$72.76	4.279%	$75.8734	$75.87	$75.85	$75.90
7 purchase totals =	$710.17		$776.2424	$776.24	$776.25	$776.30