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	$73.45	10.209%	$80.9485	$80.95	$80.95	$80.90
Purchase #2	$195.89	13.633%	$222.5957	$222.60	$222.60	$222.60
Purchase #3	$112.90	9.495%	$123.6199	$123.62	$123.60	$123.60
Purchase #4	$61.38	7.320%	$65.873	$65.87	$65.85	$65.90
Purchase #5	$41.56	12.258%	$46.6544	$46.65	$46.65	$46.70
Purchase #6	$229.85	4.543%	$240.2921	$240.29	$240.30	$240.30
Purchase #7	$52.31	3.260%	$54.0153	$54.02	$54.00	$54.00
7 purchase totals =	$767.34		$833.9989	$834.00	$833.95	$834.00