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	$11.86	8.258%	$12.8394	$12.84	$12.85	$12.80
Purchase #2	$192.72	12.270%	$216.3667	$216.37	$216.35	$216.40
Purchase #3	$125.65	13.592%	$142.7283	$142.73	$142.75	$142.70
Purchase #4	$120.87	5.394%	$127.3897	$127.39	$127.40	$127.40
Purchase #5	$190.66	9.179%	$208.1607	$208.16	$208.15	$208.20
Purchase #6	$172.70	13.514%	$196.0387	$196.04	$196.05	$196.00
Purchase #7	$130.45	10.494%	$144.1394	$144.14	$144.15	$144.10
7 purchase totals =	$944.91		$1,047.6629	$1,047.67	$1,047.70	$1,047.60