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	$19.51	8.153%	$21.1007	$21.10	$21.10	$21.10
Purchase #2	$19.66	5.630%	$20.7669	$20.77	$20.75	$20.80
Purchase #3	$185.72	4.464%	$194.0105	$194.01	$194.00	$194.00
Purchase #4	$126.72	3.818%	$131.5582	$131.56	$131.55	$131.60
Purchase #5	$131.26	12.518%	$147.6911	$147.69	$147.70	$147.70
Purchase #6	$157.36	10.522%	$173.9174	$173.92	$173.90	$173.90
Purchase #7	$113.95	12.155%	$127.8006	$127.80	$127.80	$127.80
7 purchase totals =	$754.18		$816.8454	$816.85	$816.80	$816.90