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	$153.62	4.348%	$160.2994	$160.30	$160.30	$160.30
Purchase #2	$246.53	3.640%	$255.5037	$255.50	$255.50	$255.50
Purchase #3	$135.81	8.757%	$147.7029	$147.70	$147.70	$147.70
Purchase #4	$16.83	11.155%	$18.7074	$18.71	$18.70	$18.70
Purchase #5	$93.81	6.714%	$100.1084	$100.11	$100.10	$100.10
Purchase #6	$140.31	11.420%	$156.3334	$156.33	$156.35	$156.30
Purchase #7	$91.56	10.159%	$100.8616	$100.86	$100.85	$100.90
7 purchase totals =	$878.47		$939.5168	$939.51	$939.50	$939.50