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	$27.54	4.690%	$28.8316	$28.83	$28.85	$28.80
Purchase #2	$171.46	13.468%	$194.5522	$194.55	$194.55	$194.60
Purchase #3	$101.34	10.334%	$111.8125	$111.81	$111.80	$111.80
Purchase #4	$41.38	5.494%	$43.6534	$43.65	$43.65	$43.70
Purchase #5	$97.31	8.133%	$105.2242	$105.22	$105.20	$105.20
Purchase #6	$242.26	11.831%	$270.9218	$270.92	$270.90	$270.90
Purchase #7	$135.39	7.600%	$145.6796	$145.68	$145.70	$145.70
7 purchase totals =	$816.68		$900.6753	$900.66	$900.65	$900.70