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	$51.33	12.314%	$57.6508	$57.65	$57.65	$57.70
Purchase #2	$144.70	10.641%	$160.0975	$160.10	$160.10	$160.10
Purchase #3	$26.31	11.233%	$29.2654	$29.27	$29.25	$29.30
Purchase #4	$79.25	9.490%	$86.7708	$86.77	$86.75	$86.80
Purchase #5	$60.66	11.476%	$67.6213	$67.62	$67.60	$67.60
Purchase #6	$25.42	11.495%	$28.342	$28.34	$28.35	$28.30
Purchase #7	$79.34	4.374%	$82.8103	$82.81	$82.80	$82.80
7 purchase totals =	$467.01		$512.5581	$512.56	$512.50	$512.60