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	$140.46	3.150%	$144.8845	$144.88	$144.90	$144.90
Purchase #2	$183.66	6.128%	$194.9147	$194.91	$194.90	$194.90
Purchase #3	$189.60	3.436%	$196.1147	$196.11	$196.10	$196.10
Purchase #4	$56.77	13.723%	$64.5605	$64.56	$64.55	$64.60
Purchase #5	$217.74	7.122%	$233.2474	$233.25	$233.25	$233.20
Purchase #6	$46.95	13.531%	$53.3028	$53.30	$53.30	$53.30
Purchase #7	$221.30	5.447%	$233.3542	$233.35	$233.35	$233.40
7 purchase totals =	$1,056.48		$1,120.3788	$1,120.36	$1,120.35	$1,120.40