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	$123.92	13.461%	$140.6009	$140.60	$140.60	$140.60
Purchase #2	$234.38	3.148%	$241.7583	$241.76	$241.75	$241.80
Purchase #3	$131.61	7.608%	$141.6229	$141.62	$141.60	$141.60
Purchase #4	$129.97	10.395%	$143.4804	$143.48	$143.50	$143.50
Purchase #5	$221.26	13.281%	$250.6455	$250.65	$250.65	$250.60
Purchase #6	$61.79	6.520%	$65.8187	$65.82	$65.80	$65.80
Purchase #7	$97.41	4.408%	$101.7038	$101.70	$101.70	$101.70
7 purchase totals =	$1,000.34		$1,085.6305	$1,085.63	$1,085.60	$1,085.60