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	$79.92	11.488%	$89.1012	$89.10	$89.10	$89.10
Purchase #2	$198.63	8.649%	$215.8095	$215.81	$215.80	$215.80
Purchase #3	$233.74	9.344%	$255.5807	$255.58	$255.60	$255.60
Purchase #4	$185.39	5.633%	$195.833	$195.83	$195.85	$195.80
Purchase #5	$113.35	11.560%	$126.4533	$126.45	$126.45	$126.50
Purchase #6	$240.45	9.430%	$263.1244	$263.12	$263.10	$263.10
Purchase #7	$101.72	6.599%	$108.4325	$108.43	$108.45	$108.40
7 purchase totals =	$1,153.20		$1,254.3346	$1,254.32	$1,254.35	$1,254.30