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	$72.45	12.797%	$81.7214	$81.72	$81.70	$81.70
Purchase #2	$21.54	11.573%	$24.0328	$24.03	$24.05	$24.00
Purchase #3	$105.53	5.787%	$111.637	$111.64	$111.65	$111.60
Purchase #4	$59.72	8.648%	$64.8846	$64.88	$64.90	$64.90
Purchase #5	$23.83	12.538%	$26.8178	$26.82	$26.80	$26.80
Purchase #6	$61.82	6.620%	$65.9125	$65.91	$65.90	$65.90
Purchase #7	$131.99	5.250%	$138.9195	$138.92	$138.90	$138.90
7 purchase totals =	$476.88		$513.9256	$513.92	$513.90	$513.80