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	$47.45	8.306%	$51.3912	$51.39	$51.40	$51.40
Purchase #2	$164.55	4.805%	$172.4566	$172.46	$172.45	$172.50
Purchase #3	$186.77	13.319%	$211.6459	$211.65	$211.65	$211.60
Purchase #4	$123.43	4.125%	$128.5215	$128.52	$128.50	$128.50
Purchase #5	$160.82	12.271%	$180.5542	$180.55	$180.55	$180.60
Purchase #6	$90.53	13.823%	$103.044	$103.04	$103.05	$103.00
Purchase #7	$164.62	3.465%	$170.3241	$170.32	$170.30	$170.30
7 purchase totals =	$938.17		$1,017.9375	$1,017.93	$1,017.90	$1,017.90