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	$180.72	6.699%	$192.8264	$192.83	$192.85	$192.80
Purchase #2	$9.69	8.587%	$10.5221	$10.52	$10.50	$10.50
Purchase #3	$172.41	9.199%	$188.27	$188.27	$188.25	$188.30
Purchase #4	$133.28	9.223%	$145.5724	$145.57	$145.55	$145.60
Purchase #5	$40.85	11.812%	$45.6752	$45.68	$45.70	$45.70
Purchase #6	$149.38	5.844%	$158.1098	$158.11	$158.10	$158.10
Purchase #7	$152.38	12.803%	$171.8892	$171.89	$171.90	$171.90
7 purchase totals =	$838.71		$912.8651	$912.87	$912.85	$912.90