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	$112.50	13.796%	$128.0205	$128.02	$128.00	$128.00
Purchase #2	$32.41	8.864%	$35.2828	$35.28	$35.30	$35.30
Purchase #3	$147.48	8.835%	$160.5099	$160.51	$160.50	$160.50
Purchase #4	$68.76	5.689%	$72.6718	$72.67	$72.65	$72.70
Purchase #5	$228.66	11.838%	$255.7288	$255.73	$255.75	$255.70
Purchase #6	$204.26	6.652%	$217.8474	$217.85	$217.85	$217.80
Purchase #7	$150.75	11.493%	$168.0757	$168.08	$168.10	$168.10
7 purchase totals =	$944.82		$1,038.1369	$1,038.14	$1,038.15	$1,038.10