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	$51.43	5.849%	$54.4381	$54.44	$54.45	$54.40
Purchase #2	$145.77	13.392%	$165.2915	$165.29	$165.30	$165.30
Purchase #3	$232.49	7.513%	$249.957	$249.96	$249.95	$250.00
Purchase #4	$71.70	9.659%	$78.6255	$78.63	$78.65	$78.60
Purchase #5	$191.55	10.532%	$211.724	$211.72	$211.70	$211.70
Purchase #6	$94.74	9.522%	$103.7611	$103.76	$103.75	$103.80
Purchase #7	$25.87	9.491%	$28.3253	$28.33	$28.35	$28.30
7 purchase totals =	$813.55		$892.1225	$892.13	$892.15	$892.10