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	$106.78	6.611%	$113.8392	$113.84	$113.85	$113.80
Purchase #2	$238.32	6.253%	$253.2221	$253.22	$253.20	$253.20
Purchase #3	$178.44	10.317%	$196.8497	$196.85	$196.85	$196.80
Purchase #4	$239.51	12.104%	$268.5003	$268.50	$268.50	$268.50
Purchase #5	$152.56	4.853%	$159.9637	$159.96	$159.95	$160.00
Purchase #6	$160.39	6.422%	$170.6902	$170.69	$170.70	$170.70
Purchase #7	$63.27	4.658%	$66.2171	$66.22	$66.20	$66.20
7 purchase totals =	$1,139.27		$1,229.2823	$1,229.28	$1,229.25	$1,229.20