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	$99.94	4.711%	$104.6482	$104.65	$104.65	$104.60
Purchase #2	$198.28	10.512%	$219.1232	$219.12	$219.10	$219.10
Purchase #3	$122.99	4.476%	$128.495	$128.50	$128.50	$128.50
Purchase #4	$132.30	5.740%	$139.894	$139.89	$139.90	$139.90
Purchase #5	$27.91	7.628%	$30.039	$30.04	$30.05	$30.00
Purchase #6	$139.28	3.766%	$144.5253	$144.53	$144.55	$144.50
Purchase #7	$39.64	7.312%	$42.5385	$42.54	$42.55	$42.50
7 purchase totals =	$760.34		$809.2632	$809.27	$809.30	$809.10