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	$84.77	5.192%	$89.1713	$89.17	$89.15	$89.20
Purchase #2	$82.93	10.233%	$91.4162	$91.42	$91.40	$91.40
Purchase #3	$184.47	10.572%	$203.9722	$203.97	$203.95	$204.00
Purchase #4	$72.57	12.192%	$81.4177	$81.42	$81.40	$81.40
Purchase #5	$92.98	13.719%	$105.7359	$105.74	$105.75	$105.70
Purchase #6	$109.50	10.118%	$120.5792	$120.58	$120.60	$120.60
Purchase #7	$12.30	5.706%	$13.0018	$13.00	$13.00	$13.00
7 purchase totals =	$639.52		$705.2943	$705.30	$705.25	$705.30