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	$35.55	11.713%	$39.714	$39.71	$39.70	$39.70
Purchase #2	$244.60	4.393%	$255.3453	$255.35	$255.35	$255.30
Purchase #3	$58.69	13.158%	$66.4124	$66.41	$66.40	$66.40
Purchase #4	$32.61	3.839%	$33.8619	$33.86	$33.85	$33.90
Purchase #5	$96.31	3.143%	$99.337	$99.34	$99.35	$99.30
Purchase #6	$64.51	9.673%	$70.7501	$70.75	$70.75	$70.80
Purchase #7	$53.78	3.646%	$55.7408	$55.74	$55.75	$55.70
7 purchase totals =	$586.05		$621.1615	$621.16	$621.15	$621.10