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	$147.74	13.828%	$168.1695	$168.17	$168.15	$168.20
Purchase #2	$80.78	9.681%	$88.6003	$88.60	$88.60	$88.60
Purchase #3	$38.45	10.422%	$42.4573	$42.46	$42.45	$42.50
Purchase #4	$211.27	7.326%	$226.7476	$226.75	$226.75	$226.70
Purchase #5	$229.87	10.341%	$253.6409	$253.64	$253.65	$253.60
Purchase #6	$80.74	10.771%	$89.4365	$89.44	$89.45	$89.40
Purchase #7	$157.59	10.496%	$174.1306	$174.13	$174.15	$174.10
7 purchase totals =	$946.44		$1,043.1827	$1,043.19	$1,043.20	$1,043.10