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	$235.38	11.854%	$263.2819	$263.28	$263.30	$263.30
Purchase #2	$118.40	7.516%	$127.2989	$127.30	$127.30	$127.30
Purchase #3	$151.76	5.765%	$160.509	$160.51	$160.50	$160.50
Purchase #4	$94.85	13.872%	$108.0076	$108.01	$108.00	$108.00
Purchase #5	$35.34	5.466%	$37.2717	$37.27	$37.25	$37.30
Purchase #6	$100.33	11.347%	$111.7144	$111.71	$111.70	$111.70
Purchase #7	$68.31	5.257%	$71.9011	$71.90	$71.90	$71.90
7 purchase totals =	$804.37		$879.9846	$879.98	$879.95	$880.00