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	$155.74	8.848%	$169.5199	$169.52	$169.50	$169.50
Purchase #2	$164.62	6.424%	$175.1952	$175.20	$175.20	$175.20
Purchase #3	$225.40	13.255%	$255.2768	$255.28	$255.30	$255.30
Purchase #4	$128.55	12.720%	$144.9016	$144.90	$144.90	$144.90
Purchase #5	$155.25	10.602%	$171.7096	$171.71	$171.70	$171.70
Purchase #6	$88.59	8.797%	$96.3833	$96.38	$96.40	$96.40
Purchase #7	$227.59	12.107%	$255.1443	$255.14	$255.15	$255.10
7 purchase totals =	$1,145.74		$1,268.1307	$1,268.13	$1,268.15	$1,268.10