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	$33.70	4.676%	$35.2758	$35.28	$35.30	$35.30
Purchase #2	$111.87	8.626%	$121.5199	$121.52	$121.50	$121.50
Purchase #3	$232.35	6.719%	$247.9616	$247.96	$247.95	$248.00
Purchase #4	$25.29	13.127%	$28.6098	$28.61	$28.60	$28.60
Purchase #5	$104.79	6.467%	$111.5668	$111.57	$111.55	$111.60
Purchase #6	$104.65	12.388%	$117.614	$117.61	$117.60	$117.60
Purchase #7	$242.59	9.452%	$265.5196	$265.52	$265.50	$265.50
7 purchase totals =	$855.24		$928.0675	$928.07	$928.00	$928.10