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	$49.78	9.554%	$54.536	$54.54	$54.55	$54.50
Purchase #2	$211.88	12.425%	$238.2061	$238.21	$238.20	$238.20
Purchase #3	$75.31	3.738%	$78.1251	$78.13	$78.15	$78.10
Purchase #4	$130.48	4.410%	$136.2342	$136.23	$136.25	$136.20
Purchase #5	$129.50	13.305%	$146.73	$146.73	$146.75	$146.70
Purchase #6	$31.28	7.118%	$33.5065	$33.51	$33.50	$33.50
Purchase #7	$70.84	5.658%	$74.8481	$74.85	$74.85	$74.80
7 purchase totals =	$699.07		$762.1860	$762.20	$762.25	$762.00