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	$48.88	5.654%	$51.6437	$51.64	$51.65	$51.60
Purchase #2	$88.53	12.657%	$99.7352	$99.74	$99.75	$99.70
Purchase #3	$244.98	13.142%	$277.1753	$277.18	$277.20	$277.20
Purchase #4	$148.27	8.450%	$160.7988	$160.80	$160.80	$160.80
Purchase #5	$222.51	12.754%	$250.8889	$250.89	$250.90	$250.90
Purchase #6	$220.39	12.328%	$247.5597	$247.56	$247.55	$247.60
Purchase #7	$62.82	12.871%	$70.9056	$70.91	$70.90	$70.90
7 purchase totals =	$1,036.38		$1,158.7072	$1,158.72	$1,158.75	$1,158.70