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	$10.30	4.671%	$10.7811	$10.78	$10.80	$10.80
Purchase #2	$183.48	6.852%	$196.052	$196.05	$196.05	$196.10
Purchase #3	$170.75	13.117%	$193.1473	$193.15	$193.15	$193.10
Purchase #4	$85.93	4.173%	$89.5159	$89.52	$89.50	$89.50
Purchase #5	$41.73	6.860%	$44.5927	$44.59	$44.60	$44.60
Purchase #6	$101.53	8.312%	$109.9692	$109.97	$109.95	$110.00
Purchase #7	$159.28	9.613%	$174.5916	$174.59	$174.60	$174.60
7 purchase totals =	$753.00		$818.6498	$818.65	$818.65	$818.70