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	$142.32	5.762%	$150.5205	$150.52	$150.50	$150.50
Purchase #2	$168.86	11.341%	$188.0104	$188.01	$188.00	$188.00
Purchase #3	$189.70	9.807%	$208.3039	$208.30	$208.30	$208.30
Purchase #4	$57.65	6.729%	$61.5293	$61.53	$61.55	$61.50
Purchase #5	$5.83	13.205%	$6.5999	$6.60	$6.60	$6.60
Purchase #6	$203.35	8.608%	$220.8544	$220.85	$220.85	$220.90
Purchase #7	$51.85	5.574%	$54.7401	$54.74	$54.75	$54.70
7 purchase totals =	$819.56		$890.5585	$890.55	$890.55	$890.50