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	$90.86	3.148%	$93.7203	$93.72	$93.70	$93.70
Purchase #2	$139.72	11.306%	$155.5167	$155.52	$155.50	$155.50
Purchase #3	$132.29	5.182%	$139.1453	$139.15	$139.15	$139.10
Purchase #4	$99.92	12.375%	$112.2851	$112.29	$112.30	$112.30
Purchase #5	$102.92	8.328%	$111.4912	$111.49	$111.50	$111.50
Purchase #6	$211.83	5.773%	$224.0589	$224.06	$224.05	$224.10
Purchase #7	$36.97	7.192%	$39.6289	$39.63	$39.65	$39.60
7 purchase totals =	$814.51		$875.8464	$875.86	$875.85	$875.80