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	$144.84	8.353%	$156.9385	$156.94	$156.95	$156.90
Purchase #2	$9.66	3.581%	$10.0059	$10.01	$10.00	$10.00
Purchase #3	$110.83	13.200%	$125.4596	$125.46	$125.45	$125.50
Purchase #4	$133.72	3.153%	$137.9362	$137.94	$137.95	$137.90
Purchase #5	$116.40	9.405%	$127.3474	$127.35	$127.35	$127.30
Purchase #6	$106.31	4.645%	$111.2481	$111.25	$111.25	$111.20
Purchase #7	$106.56	4.408%	$111.2572	$111.26	$111.25	$111.30
7 purchase totals =	$728.32		$780.1929	$780.21	$780.20	$780.10