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	$210.43	13.727%	$239.3157	$239.32	$239.30	$239.30
Purchase #2	$90.27	11.803%	$100.9246	$100.92	$100.90	$100.90
Purchase #3	$173.91	13.125%	$196.7357	$196.74	$196.75	$196.70
Purchase #4	$26.74	11.670%	$29.8606	$29.86	$29.85	$29.90
Purchase #5	$191.59	13.700%	$217.8378	$217.84	$217.85	$217.80
Purchase #6	$159.82	11.641%	$178.4246	$178.42	$178.40	$178.40
Purchase #7	$219.42	3.832%	$227.8282	$227.83	$227.85	$227.80
7 purchase totals =	$1,072.18		$1,190.9272	$1,190.93	$1,190.90	$1,190.80