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	$11.78	7.173%	$12.625	$12.63	$12.65	$12.60
Purchase #2	$118.40	12.350%	$133.0224	$133.02	$133.00	$133.00
Purchase #3	$107.89	3.375%	$111.5313	$111.53	$111.55	$111.50
Purchase #4	$139.99	4.554%	$146.3651	$146.37	$146.35	$146.40
Purchase #5	$136.89	4.151%	$142.5723	$142.57	$142.55	$142.60
Purchase #6	$232.32	6.780%	$248.0713	$248.07	$248.05	$248.10
Purchase #7	$103.66	9.154%	$113.149	$113.15	$113.15	$113.10
7 purchase totals =	$850.93		$907.3364	$907.34	$907.30	$907.30