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	$83.42	6.664%	$88.9791	$88.98	$89.00	$89.00
Purchase #2	$30.97	9.437%	$33.8926	$33.89	$33.90	$33.90
Purchase #3	$63.57	5.628%	$67.1477	$67.15	$67.15	$67.10
Purchase #4	$216.90	11.174%	$241.1364	$241.14	$241.15	$241.10
Purchase #5	$149.88	5.308%	$157.8356	$157.84	$157.85	$157.80
Purchase #6	$171.60	6.717%	$183.1264	$183.13	$183.15	$183.10
Purchase #7	$58.59	7.278%	$62.8542	$62.85	$62.85	$62.90
7 purchase totals =	$774.93		$834.9720	$834.98	$835.05	$834.90