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	$90.38	10.292%	$99.6819	$99.68	$99.70	$99.70
Purchase #2	$49.98	10.255%	$55.1054	$55.11	$55.10	$55.10
Purchase #3	$140.50	7.324%	$150.7902	$150.79	$150.80	$150.80
Purchase #4	$162.61	8.515%	$176.4562	$176.46	$176.45	$176.50
Purchase #5	$7.83	4.174%	$8.1568	$8.16	$8.15	$8.20
Purchase #6	$226.64	8.604%	$246.1401	$246.14	$246.15	$246.10
Purchase #7	$123.48	3.566%	$127.8833	$127.88	$127.90	$127.90
7 purchase totals =	$801.42		$864.2139	$864.22	$864.25	$864.30