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	$69.66	10.640%	$77.0718	$77.07	$77.05	$77.10
Purchase #2	$39.71	5.693%	$41.9707	$41.97	$41.95	$42.00
Purchase #3	$106.76	4.508%	$111.5727	$111.57	$111.55	$111.60
Purchase #4	$57.54	8.872%	$62.6449	$62.64	$62.65	$62.60
Purchase #5	$143.29	8.490%	$155.4553	$155.46	$155.45	$155.50
Purchase #6	$154.49	9.223%	$168.7386	$168.74	$168.75	$168.70
Purchase #7	$71.59	8.581%	$77.7331	$77.73	$77.75	$77.70
7 purchase totals =	$643.04		$695.1871	$695.18	$695.15	$695.20