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	$86.45	5.167%	$90.9169	$90.92	$90.90	$90.90
Purchase #2	$19.99	10.448%	$22.0786	$22.08	$22.10	$22.10
Purchase #3	$29.90	4.483%	$31.2404	$31.24	$31.25	$31.20
Purchase #4	$113.46	11.274%	$126.2515	$126.25	$126.25	$126.30
Purchase #5	$193.53	7.203%	$207.47	$207.47	$207.45	$207.50
Purchase #6	$205.55	13.570%	$233.4431	$233.44	$233.45	$233.40
Purchase #7	$83.77	7.572%	$90.1131	$90.11	$90.10	$90.10
7 purchase totals =	$732.65		$801.5136	$801.51	$801.50	$801.50