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	$215.66	3.573%	$223.3655	$223.37	$223.35	$223.40
Purchase #2	$173.69	8.398%	$188.2765	$188.28	$188.30	$188.30
Purchase #3	$81.80	11.702%	$91.3722	$91.37	$91.35	$91.40
Purchase #4	$101.43	11.201%	$112.7912	$112.79	$112.80	$112.80
Purchase #5	$84.52	5.459%	$89.1339	$89.13	$89.15	$89.10
Purchase #6	$121.50	9.268%	$132.7606	$132.76	$132.75	$132.80
Purchase #7	$80.71	11.719%	$90.1684	$90.17	$90.15	$90.20
7 purchase totals =	$859.31		$927.8683	$927.87	$927.85	$928.00