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	$73.77	11.360%	$82.1503	$82.15	$82.15	$82.20
Purchase #2	$99.93	11.338%	$111.2601	$111.26	$111.25	$111.30
Purchase #3	$66.59	6.834%	$71.1408	$71.14	$71.15	$71.10
Purchase #4	$207.52	3.251%	$214.2665	$214.27	$214.25	$214.30
Purchase #5	$131.28	6.318%	$139.5743	$139.57	$139.55	$139.60
Purchase #6	$162.36	11.413%	$180.8901	$180.89	$180.90	$180.90
Purchase #7	$18.77	4.647%	$19.6422	$19.64	$19.65	$19.60
7 purchase totals =	$760.22		$818.9243	$818.92	$818.90	$819.00