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	$89.43	12.187%	$100.3288	$100.33	$100.35	$100.30
Purchase #2	$172.45	3.639%	$178.7255	$178.73	$178.75	$178.70
Purchase #3	$199.94	13.733%	$227.3978	$227.40	$227.40	$227.40
Purchase #4	$124.31	10.431%	$137.2768	$137.28	$137.30	$137.30
Purchase #5	$114.89	7.511%	$123.5194	$123.52	$123.50	$123.50
Purchase #6	$236.94	8.701%	$257.5561	$257.56	$257.55	$257.60
Purchase #7	$171.86	10.374%	$189.6888	$189.69	$189.70	$189.70
7 purchase totals =	$1,109.82		$1,214.4932	$1,214.51	$1,214.55	$1,214.50