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	$91.31	8.604%	$99.1663	$99.17	$99.15	$99.20
Purchase #2	$191.44	4.605%	$200.2558	$200.26	$200.25	$200.30
Purchase #3	$34.83	6.719%	$37.1702	$37.17	$37.15	$37.20
Purchase #4	$65.33	8.551%	$70.9164	$70.92	$70.90	$70.90
Purchase #5	$140.31	4.858%	$147.1263	$147.13	$147.15	$147.10
Purchase #6	$225.32	13.453%	$255.6323	$255.63	$255.65	$255.60
Purchase #7	$88.34	9.550%	$96.7765	$96.78	$96.80	$96.80
7 purchase totals =	$836.88		$907.0438	$907.06	$907.05	$907.10