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	$188.85	13.642%	$214.6129	$214.61	$214.60	$214.60
Purchase #2	$107.61	11.281%	$119.7495	$119.75	$119.75	$119.70
Purchase #3	$124.76	3.308%	$128.8871	$128.89	$128.90	$128.90
Purchase #4	$89.49	11.356%	$99.6525	$99.65	$99.65	$99.70
Purchase #5	$143.28	5.325%	$150.9097	$150.91	$150.90	$150.90
Purchase #6	$79.72	3.631%	$82.6146	$82.61	$82.60	$82.60
Purchase #7	$21.93	5.874%	$23.2182	$23.22	$23.20	$23.20
7 purchase totals =	$755.64		$819.6445	$819.64	$819.60	$819.60