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	$52.35	10.690%	$57.9462	$57.95	$57.95	$57.90
Purchase #2	$172.34	5.375%	$181.6033	$181.60	$181.60	$181.60
Purchase #3	$159.90	7.739%	$172.2747	$172.27	$172.25	$172.30
Purchase #4	$18.72	11.801%	$20.9291	$20.93	$20.95	$20.90
Purchase #5	$19.75	7.756%	$21.2818	$21.28	$21.30	$21.30
Purchase #6	$203.62	6.360%	$216.5702	$216.57	$216.55	$216.60
Purchase #7	$113.30	9.246%	$123.7757	$123.78	$123.80	$123.80
7 purchase totals =	$739.98		$794.3810	$794.38	$794.40	$794.40