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	$133.56	11.364%	$148.7378	$148.74	$148.75	$148.70
Purchase #2	$145.57	7.584%	$156.61	$156.61	$156.60	$156.60
Purchase #3	$84.91	8.213%	$91.8837	$91.88	$91.90	$91.90
Purchase #4	$84.96	4.842%	$89.0738	$89.07	$89.05	$89.10
Purchase #5	$70.39	9.461%	$77.0496	$77.05	$77.05	$77.00
Purchase #6	$49.35	8.178%	$53.3858	$53.39	$53.40	$53.40
Purchase #7	$203.82	8.829%	$221.8153	$221.82	$221.80	$221.80
7 purchase totals =	$772.56		$838.5560	$838.56	$838.55	$838.50