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	$247.51	5.799%	$261.8631	$261.86	$261.85	$261.90
Purchase #2	$230.63	10.176%	$254.0989	$254.10	$254.10	$254.10
Purchase #3	$86.31	11.125%	$95.912	$95.91	$95.90	$95.90
Purchase #4	$22.33	6.497%	$23.7808	$23.78	$23.80	$23.80
Purchase #5	$31.39	10.123%	$34.5676	$34.57	$34.55	$34.60
Purchase #6	$82.69	9.373%	$90.4405	$90.44	$90.45	$90.40
Purchase #7	$210.90	10.709%	$233.4853	$233.49	$233.50	$233.50
7 purchase totals =	$911.76		$994.1482	$994.15	$994.15	$994.20