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	$80.41	5.109%	$84.5181	$84.52	$84.50	$84.50
Purchase #2	$231.73	13.628%	$263.3102	$263.31	$263.30	$263.30
Purchase #3	$105.62	10.748%	$116.972	$116.97	$116.95	$117.00
Purchase #4	$172.32	12.409%	$193.7032	$193.70	$193.70	$193.70
Purchase #5	$170.88	10.573%	$188.9471	$188.95	$188.95	$188.90
Purchase #6	$126.63	4.162%	$131.9003	$131.90	$131.90	$131.90
Purchase #7	$32.57	13.791%	$37.0617	$37.06	$37.05	$37.10
7 purchase totals =	$920.16		$1,016.4126	$1,016.41	$1,016.35	$1,016.40