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	$34.56	11.378%	$38.4922	$38.49	$38.50	$38.50
Purchase #2	$58.27	3.543%	$60.3345	$60.33	$60.35	$60.30
Purchase #3	$76.71	4.412%	$80.0944	$80.09	$80.10	$80.10
Purchase #4	$250.34	6.695%	$267.1003	$267.10	$267.10	$267.10
Purchase #5	$160.59	7.477%	$172.5973	$172.60	$172.60	$172.60
Purchase #6	$47.58	10.316%	$52.4884	$52.49	$52.50	$52.50
Purchase #7	$179.83	11.560%	$200.6183	$200.62	$200.60	$200.60
7 purchase totals =	$807.88		$871.7254	$871.72	$871.75	$871.70