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	$26.91	4.224%	$28.0467	$28.05	$28.05	$28.00
Purchase #2	$207.89	11.815%	$232.4522	$232.45	$232.45	$232.50
Purchase #3	$97.76	5.276%	$102.9178	$102.92	$102.90	$102.90
Purchase #4	$55.36	6.667%	$59.0509	$59.05	$59.05	$59.10
Purchase #5	$29.90	12.422%	$33.6142	$33.61	$33.60	$33.60
Purchase #6	$154.61	6.159%	$164.1324	$164.13	$164.15	$164.10
Purchase #7	$86.70	4.451%	$90.559	$90.56	$90.55	$90.60
7 purchase totals =	$659.13		$710.7732	$710.77	$710.75	$710.80