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	$14.42	10.253%	$15.8985	$15.90	$15.90	$15.90
Purchase #2	$32.27	3.281%	$33.3288	$33.33	$33.35	$33.30
Purchase #3	$96.86	4.428%	$101.149	$101.15	$101.15	$101.10
Purchase #4	$178.52	3.648%	$185.0324	$185.03	$185.05	$185.00
Purchase #5	$158.38	3.301%	$163.6081	$163.61	$163.60	$163.60
Purchase #6	$250.45	3.716%	$259.7567	$259.76	$259.75	$259.80
Purchase #7	$109.51	6.405%	$116.5241	$116.52	$116.50	$116.50
7 purchase totals =	$840.41		$875.2976	$875.30	$875.30	$875.20