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	$85.97	4.838%	$90.1292	$90.13	$90.15	$90.10
Purchase #2	$28.85	11.476%	$32.1608	$32.16	$32.15	$32.20
Purchase #3	$167.98	12.139%	$188.3711	$188.37	$188.35	$188.40
Purchase #4	$232.58	11.523%	$259.3802	$259.38	$259.40	$259.40
Purchase #5	$174.69	8.362%	$189.2976	$189.30	$189.30	$189.30
Purchase #6	$117.50	7.756%	$126.6133	$126.61	$126.60	$126.60
Purchase #7	$65.43	6.854%	$69.9146	$69.91	$69.90	$69.90
7 purchase totals =	$873.00		$955.8668	$955.86	$955.85	$955.90