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	$218.97	10.309%	$241.5436	$241.54	$241.55	$241.50
Purchase #2	$189.82	10.198%	$209.1778	$209.18	$209.20	$209.20
Purchase #3	$54.27	13.145%	$61.4038	$61.40	$61.40	$61.40
Purchase #4	$10.66	4.420%	$11.1312	$11.13	$11.15	$11.10
Purchase #5	$158.94	7.650%	$171.0989	$171.10	$171.10	$171.10
Purchase #6	$80.71	11.201%	$89.7503	$89.75	$89.75	$89.80
Purchase #7	$52.82	5.759%	$55.8619	$55.86	$55.85	$55.90
7 purchase totals =	$766.19		$839.9675	$839.96	$840.00	$840.00