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	$35.52	3.781%	$36.863	$36.86	$36.85	$36.90
Purchase #2	$130.37	12.367%	$146.4929	$146.49	$146.50	$146.50
Purchase #3	$109.66	5.119%	$115.2735	$115.27	$115.25	$115.30
Purchase #4	$158.28	9.458%	$173.2501	$173.25	$173.25	$173.30
Purchase #5	$197.42	6.245%	$209.7489	$209.75	$209.75	$209.70
Purchase #6	$56.69	7.812%	$61.1186	$61.12	$61.10	$61.10
Purchase #7	$80.87	10.730%	$89.5474	$89.55	$89.55	$89.50
7 purchase totals =	$768.81		$832.2944	$832.29	$832.25	$832.30