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	$114.68	12.464%	$128.9737	$128.97	$128.95	$129.00
Purchase #2	$79.58	7.499%	$85.5477	$85.55	$85.55	$85.50
Purchase #3	$186.69	7.274%	$200.2698	$200.27	$200.25	$200.30
Purchase #4	$124.44	10.640%	$137.6804	$137.68	$137.70	$137.70
Purchase #5	$121.38	6.497%	$129.2661	$129.27	$129.25	$129.30
Purchase #6	$101.55	10.174%	$111.8817	$111.88	$111.90	$111.90
Purchase #7	$68.56	13.481%	$77.8026	$77.80	$77.80	$77.80
7 purchase totals =	$796.88		$871.4220	$871.42	$871.40	$871.50