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	$86.91	4.628%	$90.9322	$90.93	$90.95	$90.90
Purchase #2	$134.31	6.647%	$143.2376	$143.24	$143.25	$143.20
Purchase #3	$60.31	13.664%	$68.5508	$68.55	$68.55	$68.60
Purchase #4	$235.43	7.544%	$253.1908	$253.19	$253.20	$253.20
Purchase #5	$214.59	11.160%	$238.5382	$238.54	$238.55	$238.50
Purchase #6	$55.95	6.471%	$59.5705	$59.57	$59.55	$59.60
Purchase #7	$74.26	3.250%	$76.6735	$76.67	$76.65	$76.70
7 purchase totals =	$861.76		$930.6936	$930.69	$930.70	$930.70