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	$180.69	6.364%	$192.1891	$192.19	$192.20	$192.20
Purchase #2	$78.92	5.287%	$83.0925	$83.09	$83.10	$83.10
Purchase #3	$64.67	12.247%	$72.5901	$72.59	$72.60	$72.60
Purchase #4	$105.70	11.437%	$117.7889	$117.79	$117.80	$117.80
Purchase #5	$73.59	6.754%	$78.5603	$78.56	$78.55	$78.60
Purchase #6	$94.67	12.527%	$106.5293	$106.53	$106.55	$106.50
Purchase #7	$68.52	8.173%	$74.1201	$74.12	$74.10	$74.10
7 purchase totals =	$666.76		$724.8703	$724.87	$724.90	$724.90