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	$102.90	12.127%	$115.3787	$115.38	$115.40	$115.40
Purchase #2	$64.36	10.572%	$71.1641	$71.16	$71.15	$71.20
Purchase #3	$24.81	13.243%	$28.0956	$28.10	$28.10	$28.10
Purchase #4	$97.79	13.558%	$111.0484	$111.05	$111.05	$111.00
Purchase #5	$211.43	3.472%	$218.7708	$218.77	$218.75	$218.80
Purchase #6	$117.77	4.580%	$123.1639	$123.16	$123.15	$123.20
Purchase #7	$226.26	13.451%	$256.6942	$256.69	$256.70	$256.70
7 purchase totals =	$845.32		$924.3157	$924.31	$924.30	$924.40