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	$133.32	12.518%	$150.009	$150.01	$150.00	$150.00
Purchase #2	$249.71	13.566%	$283.5857	$283.59	$283.60	$283.60
Purchase #3	$53.55	6.236%	$56.8894	$56.89	$56.90	$56.90
Purchase #4	$245.41	11.364%	$273.2984	$273.30	$273.30	$273.30
Purchase #5	$248.67	8.694%	$270.2894	$270.29	$270.30	$270.30
Purchase #6	$120.26	10.514%	$132.9041	$132.90	$132.90	$132.90
Purchase #7	$165.70	4.133%	$172.5484	$172.55	$172.55	$172.50
7 purchase totals =	$1,216.62		$1,339.5244	$1,339.53	$1,339.55	$1,339.50