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	$102.51	8.782%	$111.5124	$111.51	$111.50	$111.50
Purchase #2	$159.64	12.168%	$179.065	$179.07	$179.05	$179.10
Purchase #3	$75.73	5.815%	$80.1337	$80.13	$80.15	$80.10
Purchase #4	$148.88	12.500%	$167.49	$167.49	$167.50	$167.50
Purchase #5	$49.98	12.525%	$56.24	$56.24	$56.25	$56.20
Purchase #6	$149.26	8.609%	$162.1098	$162.11	$162.10	$162.10
Purchase #7	$132.56	8.235%	$143.4763	$143.48	$143.50	$143.50
7 purchase totals =	$818.56		$900.0272	$900.03	$900.05	$900.00