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	$240.75	5.512%	$254.0201	$254.02	$254.00	$254.00
Purchase #2	$120.75	5.360%	$127.2222	$127.22	$127.20	$127.20
Purchase #3	$6.94	9.375%	$7.5906	$7.59	$7.60	$7.60
Purchase #4	$101.72	10.826%	$112.7322	$112.73	$112.75	$112.70
Purchase #5	$82.48	5.594%	$87.0939	$87.09	$87.10	$87.10
Purchase #6	$73.75	11.805%	$82.4562	$82.46	$82.45	$82.50
Purchase #7	$161.34	6.716%	$172.1756	$172.18	$172.20	$172.20
7 purchase totals =	$787.73		$843.2908	$843.29	$843.30	$843.30