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	$117.89	7.108%	$126.2696	$126.27	$126.25	$126.30
Purchase #2	$178.94	5.274%	$188.3773	$188.38	$188.40	$188.40
Purchase #3	$165.48	4.118%	$172.2945	$172.29	$172.30	$172.30
Purchase #4	$60.36	12.830%	$68.1042	$68.10	$68.10	$68.10
Purchase #5	$76.33	7.852%	$82.3234	$82.32	$82.30	$82.30
Purchase #6	$46.61	11.717%	$52.0713	$52.07	$52.05	$52.10
Purchase #7	$69.87	10.610%	$77.2832	$77.28	$77.30	$77.30
7 purchase totals =	$715.48		$766.7235	$766.71	$766.70	$766.80