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	$33.73	10.797%	$37.3718	$37.37	$37.35	$37.40
Purchase #2	$112.58	9.396%	$123.158	$123.16	$123.15	$123.20
Purchase #3	$33.64	10.823%	$37.2809	$37.28	$37.30	$37.30
Purchase #4	$239.56	6.674%	$255.5482	$255.55	$255.55	$255.50
Purchase #5	$175.40	8.809%	$190.851	$190.85	$190.85	$190.90
Purchase #6	$50.55	9.688%	$55.4473	$55.45	$55.45	$55.40
Purchase #7	$132.94	12.476%	$149.5256	$149.53	$149.55	$149.50
7 purchase totals =	$778.40		$849.1828	$849.19	$849.20	$849.20