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	$161.89	6.451%	$172.3335	$172.33	$172.35	$172.30
Purchase #2	$161.55	13.780%	$183.8116	$183.81	$183.80	$183.80
Purchase #3	$10.37	6.174%	$11.0102	$11.01	$11.00	$11.00
Purchase #4	$96.58	7.112%	$103.4488	$103.45	$103.45	$103.40
Purchase #5	$140.25	8.817%	$152.6158	$152.62	$152.60	$152.60
Purchase #6	$81.28	9.674%	$89.143	$89.14	$89.15	$89.10
Purchase #7	$5.33	9.759%	$5.8502	$5.85	$5.85	$5.90
7 purchase totals =	$657.25		$718.2131	$718.21	$718.20	$718.10