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	$88.79	13.364%	$100.6559	$100.66	$100.65	$100.70
Purchase #2	$110.56	5.606%	$116.758	$116.76	$116.75	$116.80
Purchase #3	$166.71	5.638%	$176.1091	$176.11	$176.10	$176.10
Purchase #4	$104.36	7.370%	$112.0513	$112.05	$112.05	$112.10
Purchase #5	$118.34	10.316%	$130.548	$130.55	$130.55	$130.50
Purchase #6	$37.71	7.496%	$40.5367	$40.54	$40.55	$40.50
Purchase #7	$13.46	9.831%	$14.7833	$14.78	$14.80	$14.80
7 purchase totals =	$639.93		$691.4423	$691.45	$691.45	$691.50