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	$73.50	13.129%	$83.1498	$83.15	$83.15	$83.10
Purchase #2	$72.32	6.663%	$77.1387	$77.14	$77.15	$77.10
Purchase #3	$201.72	10.608%	$223.1185	$223.12	$223.10	$223.10
Purchase #4	$43.92	3.830%	$45.6021	$45.60	$45.60	$45.60
Purchase #5	$181.82	6.180%	$193.0565	$193.06	$193.05	$193.10
Purchase #6	$131.50	7.149%	$140.9009	$140.90	$140.90	$140.90
Purchase #7	$187.51	4.800%	$196.5105	$196.51	$196.50	$196.50
7 purchase totals =	$892.29		$959.4770	$959.48	$959.45	$959.40