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	$37.61	12.852%	$42.4436	$42.44	$42.45	$42.40
Purchase #2	$123.95	3.707%	$128.5448	$128.54	$128.55	$128.50
Purchase #3	$146.28	3.706%	$151.7011	$151.70	$151.70	$151.70
Purchase #4	$168.26	13.781%	$191.4479	$191.45	$191.45	$191.40
Purchase #5	$194.87	10.562%	$215.4522	$215.45	$215.45	$215.50
Purchase #6	$89.99	10.339%	$99.2941	$99.29	$99.30	$99.30
Purchase #7	$173.78	8.655%	$188.8207	$188.82	$188.80	$188.80
7 purchase totals =	$934.74		$1,017.7044	$1,017.69	$1,017.70	$1,017.60