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	$84.29	6.460%	$89.7351	$89.74	$89.75	$89.70
Purchase #2	$153.73	8.620%	$166.9815	$166.98	$167.00	$167.00
Purchase #3	$164.52	3.846%	$170.8474	$170.85	$170.85	$170.80
Purchase #4	$151.80	10.578%	$167.8574	$167.86	$167.85	$167.90
Purchase #5	$143.41	4.321%	$149.6067	$149.61	$149.60	$149.60
Purchase #6	$19.41	6.250%	$20.6231	$20.62	$20.60	$20.60
Purchase #7	$86.70	6.528%	$92.3598	$92.36	$92.35	$92.40
7 purchase totals =	$803.86		$858.0110	$858.02	$858.00	$858.00