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	$83.47	8.212%	$90.3246	$90.32	$90.30	$90.30
Purchase #2	$41.72	3.140%	$43.03	$43.03	$43.05	$43.00
Purchase #3	$71.69	5.401%	$75.562	$75.56	$75.55	$75.60
Purchase #4	$158.45	10.716%	$175.4295	$175.43	$175.45	$175.40
Purchase #5	$248.62	13.551%	$282.3105	$282.31	$282.30	$282.30
Purchase #6	$150.69	3.474%	$155.925	$155.93	$155.95	$155.90
Purchase #7	$76.31	6.339%	$81.1473	$81.15	$81.15	$81.10
7 purchase totals =	$830.95		$903.7289	$903.73	$903.75	$903.60