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	$82.56	9.548%	$90.4428	$90.44	$90.45	$90.40
Purchase #2	$135.56	3.819%	$140.737	$140.74	$140.75	$140.70
Purchase #3	$123.86	6.309%	$131.6743	$131.67	$131.65	$131.70
Purchase #4	$11.90	9.265%	$13.0025	$13.00	$13.00	$13.00
Purchase #5	$102.45	8.470%	$111.1275	$111.13	$111.15	$111.10
Purchase #6	$97.86	10.590%	$108.2234	$108.22	$108.20	$108.20
Purchase #7	$103.43	11.433%	$115.2552	$115.26	$115.25	$115.30
7 purchase totals =	$657.62		$710.4627	$710.46	$710.45	$710.40