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	$95.77	4.498%	$100.0777	$100.08	$100.10	$100.10
Purchase #2	$217.28	12.434%	$244.2966	$244.30	$244.30	$244.30
Purchase #3	$202.62	6.243%	$215.2696	$215.27	$215.25	$215.30
Purchase #4	$249.37	12.776%	$281.2295	$281.23	$281.25	$281.20
Purchase #5	$209.83	4.819%	$219.9417	$219.94	$219.95	$219.90
Purchase #6	$39.60	4.248%	$41.2822	$41.28	$41.30	$41.30
Purchase #7	$176.39	12.302%	$198.0895	$198.09	$198.10	$198.10
7 purchase totals =	$1,190.86		$1,300.1868	$1,300.19	$1,300.25	$1,300.20