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	$152.46	3.738%	$158.159	$158.16	$158.15	$158.20
Purchase #2	$200.94	10.807%	$222.6556	$222.66	$222.65	$222.70
Purchase #3	$33.98	9.570%	$37.2319	$37.23	$37.25	$37.20
Purchase #4	$230.70	8.736%	$250.854	$250.85	$250.85	$250.90
Purchase #5	$145.48	4.530%	$152.0702	$152.07	$152.05	$152.10
Purchase #6	$99.41	13.351%	$112.6822	$112.68	$112.70	$112.70
Purchase #7	$37.64	11.611%	$42.0104	$42.01	$42.00	$42.00
7 purchase totals =	$900.61		$975.6633	$975.66	$975.65	$975.80