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	$55.99	6.608%	$59.6898	$59.69	$59.70	$59.70
Purchase #2	$103.82	5.425%	$109.4522	$109.45	$109.45	$109.50
Purchase #3	$99.89	6.593%	$106.4757	$106.48	$106.50	$106.50
Purchase #4	$247.91	13.768%	$282.0422	$282.04	$282.05	$282.00
Purchase #5	$116.91	9.621%	$128.1579	$128.16	$128.15	$128.20
Purchase #6	$44.25	13.611%	$50.2729	$50.27	$50.25	$50.30
Purchase #7	$140.57	8.433%	$152.4243	$152.42	$152.40	$152.40
7 purchase totals =	$809.34		$888.5150	$888.51	$888.50	$888.60