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	$127.68	11.312%	$142.1232	$142.12	$142.10	$142.10
Purchase #2	$119.76	3.811%	$124.3241	$124.32	$124.30	$124.30
Purchase #3	$226.73	10.840%	$251.3075	$251.31	$251.30	$251.30
Purchase #4	$49.83	10.468%	$55.0462	$55.05	$55.05	$55.00
Purchase #5	$219.72	7.538%	$236.2825	$236.28	$236.30	$236.30
Purchase #6	$113.73	6.310%	$120.9064	$120.91	$120.90	$120.90
Purchase #7	$31.44	3.437%	$32.5206	$32.52	$32.50	$32.50
7 purchase totals =	$888.89		$962.5105	$962.51	$962.45	$962.40