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	$138.91	6.465%	$147.8905	$147.89	$147.90	$147.90
Purchase #2	$119.74	7.228%	$128.3948	$128.39	$128.40	$128.40
Purchase #3	$229.26	13.621%	$260.4875	$260.49	$260.50	$260.50
Purchase #4	$82.83	4.581%	$86.6244	$86.62	$86.60	$86.60
Purchase #5	$87.55	9.731%	$96.0695	$96.07	$96.05	$96.10
Purchase #6	$63.43	12.634%	$71.4437	$71.44	$71.45	$71.40
Purchase #7	$85.32	8.577%	$92.6379	$92.64	$92.65	$92.60
7 purchase totals =	$807.04		$883.5483	$883.54	$883.55	$883.50