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	$165.43	5.292%	$174.1846	$174.18	$174.20	$174.20
Purchase #2	$137.44	13.821%	$156.4356	$156.44	$156.45	$156.40
Purchase #3	$152.87	3.513%	$158.2403	$158.24	$158.25	$158.20
Purchase #4	$39.53	7.130%	$42.3485	$42.35	$42.35	$42.30
Purchase #5	$53.56	4.236%	$55.8288	$55.83	$55.85	$55.80
Purchase #6	$28.90	12.628%	$32.5495	$32.55	$32.55	$32.50
Purchase #7	$161.55	8.136%	$174.6937	$174.69	$174.70	$174.70
7 purchase totals =	$739.28		$794.2810	$794.28	$794.35	$794.10