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	$83.51	12.679%	$94.0982	$94.10	$94.10	$94.10
Purchase #2	$59.38	8.595%	$64.4837	$64.48	$64.50	$64.50
Purchase #3	$73.41	13.799%	$83.5398	$83.54	$83.55	$83.50
Purchase #4	$138.52	10.820%	$153.5079	$153.51	$153.50	$153.50
Purchase #5	$134.78	3.538%	$139.5485	$139.55	$139.55	$139.50
Purchase #6	$185.78	5.670%	$196.3137	$196.31	$196.30	$196.30
Purchase #7	$129.89	13.111%	$146.9199	$146.92	$146.90	$146.90
7 purchase totals =	$805.27		$878.4117	$878.41	$878.40	$878.30