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	$90.44	11.586%	$100.9184	$100.92	$100.90	$100.90
Purchase #2	$6.49	10.102%	$7.1456	$7.15	$7.15	$7.10
Purchase #3	$106.44	11.183%	$118.3432	$118.34	$118.35	$118.30
Purchase #4	$132.91	9.548%	$145.6002	$145.60	$145.60	$145.60
Purchase #5	$90.52	10.315%	$99.8571	$99.86	$99.85	$99.90
Purchase #6	$125.63	8.609%	$136.4455	$136.45	$136.45	$136.40
Purchase #7	$250.36	8.785%	$272.3541	$272.35	$272.35	$272.40
7 purchase totals =	$802.79		$880.6641	$880.67	$880.65	$880.60