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	$142.34	11.631%	$158.8956	$158.90	$158.90	$158.90
Purchase #2	$124.85	9.332%	$136.501	$136.50	$136.50	$136.50
Purchase #3	$198.58	9.736%	$217.9137	$217.91	$217.90	$217.90
Purchase #4	$149.70	6.719%	$159.7583	$159.76	$159.75	$159.80
Purchase #5	$130.33	5.525%	$137.5307	$137.53	$137.55	$137.50
Purchase #6	$89.94	12.820%	$101.4703	$101.47	$101.45	$101.50
Purchase #7	$17.85	13.558%	$20.2701	$20.27	$20.25	$20.30
7 purchase totals =	$853.59		$932.3397	$932.34	$932.30	$932.40