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	$36.63	3.323%	$37.8472	$37.85	$37.85	$37.80
Purchase #2	$159.62	8.102%	$172.5524	$172.55	$172.55	$172.60
Purchase #3	$155.52	7.559%	$167.2758	$167.28	$167.30	$167.30
Purchase #4	$166.65	13.466%	$189.0911	$189.09	$189.10	$189.10
Purchase #5	$155.35	10.348%	$171.4256	$171.43	$171.45	$171.40
Purchase #6	$235.54	8.411%	$255.3513	$255.35	$255.35	$255.40
Purchase #7	$80.49	6.749%	$85.9223	$85.92	$85.90	$85.90
7 purchase totals =	$989.80		$1,079.4657	$1,079.47	$1,079.50	$1,079.50