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	$122.42	12.197%	$137.3516	$137.35	$137.35	$137.40
Purchase #2	$109.34	13.606%	$124.2168	$124.22	$124.20	$124.20
Purchase #3	$39.85	11.629%	$44.4842	$44.48	$44.50	$44.50
Purchase #4	$242.42	6.485%	$258.1409	$258.14	$258.15	$258.10
Purchase #5	$42.52	13.177%	$48.1229	$48.12	$48.10	$48.10
Purchase #6	$161.29	8.712%	$175.3416	$175.34	$175.35	$175.30
Purchase #7	$220.56	3.617%	$228.5377	$228.54	$228.55	$228.50
7 purchase totals =	$938.40		$1,016.1957	$1,016.19	$1,016.20	$1,016.10