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	$129.40	13.359%	$146.6865	$146.69	$146.70	$146.70
Purchase #2	$73.73	7.328%	$79.1329	$79.13	$79.15	$79.10
Purchase #3	$83.97	8.672%	$91.2519	$91.25	$91.25	$91.30
Purchase #4	$68.89	13.114%	$77.9242	$77.92	$77.90	$77.90
Purchase #5	$177.88	10.477%	$196.5165	$196.52	$196.50	$196.50
Purchase #6	$54.72	13.682%	$62.2068	$62.21	$62.20	$62.20
Purchase #7	$50.88	12.781%	$57.383	$57.38	$57.40	$57.40
7 purchase totals =	$639.47		$711.1018	$711.10	$711.10	$711.10