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	$47.63	6.737%	$50.8388	$50.84	$50.85	$50.80
Purchase #2	$129.74	11.353%	$144.4694	$144.47	$144.45	$144.50
Purchase #3	$82.80	12.105%	$92.8229	$92.82	$92.80	$92.80
Purchase #4	$230.46	4.208%	$240.1578	$240.16	$240.15	$240.20
Purchase #5	$20.37	4.361%	$21.2583	$21.26	$21.25	$21.30
Purchase #6	$88.33	12.656%	$99.509	$99.51	$99.50	$99.50
Purchase #7	$105.53	4.599%	$110.3833	$110.38	$110.40	$110.40
7 purchase totals =	$704.86		$759.4395	$759.44	$759.40	$759.50