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	$95.65	4.563%	$100.0145	$100.01	$100.00	$100.00
Purchase #2	$27.94	9.155%	$30.4979	$30.50	$30.50	$30.50
Purchase #3	$95.38	5.521%	$100.6459	$100.65	$100.65	$100.60
Purchase #4	$172.98	13.303%	$195.9915	$195.99	$196.00	$196.00
Purchase #5	$91.99	6.858%	$98.2987	$98.30	$98.30	$98.30
Purchase #6	$83.27	6.830%	$88.9573	$88.96	$88.95	$89.00
Purchase #7	$127.85	8.783%	$139.0791	$139.08	$139.10	$139.10
7 purchase totals =	$695.06		$753.4849	$753.49	$753.50	$753.50