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	$143.26	12.256%	$160.8179	$160.82	$160.80	$160.80
Purchase #2	$80.71	11.818%	$90.2483	$90.25	$90.25	$90.20
Purchase #3	$115.71	13.440%	$131.2614	$131.26	$131.25	$131.30
Purchase #4	$250.43	8.431%	$271.5438	$271.54	$271.55	$271.50
Purchase #5	$45.48	4.678%	$47.6076	$47.61	$47.60	$47.60
Purchase #6	$222.71	12.456%	$250.4508	$250.45	$250.45	$250.50
Purchase #7	$95.89	13.583%	$108.9147	$108.91	$108.90	$108.90
7 purchase totals =	$954.19		$1,060.8445	$1,060.84	$1,060.80	$1,060.80