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	$231.77	3.472%	$239.8171	$239.82	$239.80	$239.80
Purchase #2	$79.75	12.629%	$89.8216	$89.82	$89.80	$89.80
Purchase #3	$52.72	6.506%	$56.15	$56.15	$56.15	$56.20
Purchase #4	$174.33	13.267%	$197.4584	$197.46	$197.45	$197.50
Purchase #5	$248.39	10.515%	$274.5082	$274.51	$274.50	$274.50
Purchase #6	$200.30	5.492%	$211.3005	$211.30	$211.30	$211.30
Purchase #7	$186.67	13.769%	$212.3726	$212.37	$212.35	$212.40
7 purchase totals =	$1,173.93		$1,281.4284	$1,281.43	$1,281.35	$1,281.50