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	$18.91	6.626%	$20.163	$20.16	$20.15	$20.20
Purchase #2	$53.50	5.759%	$56.5811	$56.58	$56.60	$56.60
Purchase #3	$79.42	5.505%	$83.7921	$83.79	$83.80	$83.80
Purchase #4	$82.95	9.343%	$90.7	$90.70	$90.70	$90.70
Purchase #5	$128.33	12.180%	$143.9606	$143.96	$143.95	$144.00
Purchase #6	$5.31	12.185%	$5.957	$5.96	$5.95	$6.00
Purchase #7	$154.59	9.401%	$169.123	$169.12	$169.10	$169.10
7 purchase totals =	$523.01		$570.2768	$570.27	$570.25	$570.40