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	$83.84	6.686%	$89.4455	$89.45	$89.45	$89.40
Purchase #2	$209.62	6.749%	$223.7673	$223.77	$223.75	$223.80
Purchase #3	$235.37	11.595%	$262.6612	$262.66	$262.65	$262.70
Purchase #4	$250.95	9.874%	$275.7288	$275.73	$275.75	$275.70
Purchase #5	$62.69	13.217%	$70.9757	$70.98	$71.00	$71.00
Purchase #6	$200.82	10.661%	$222.2294	$222.23	$222.25	$222.20
Purchase #7	$198.87	12.346%	$223.4225	$223.42	$223.40	$223.40
7 purchase totals =	$1,242.16		$1,368.2304	$1,368.24	$1,368.25	$1,368.20