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	$153.73	12.383%	$172.7664	$172.77	$172.75	$172.80
Purchase #2	$131.94	9.309%	$144.2223	$144.22	$144.20	$144.20
Purchase #3	$38.65	10.762%	$42.8095	$42.81	$42.80	$42.80
Purchase #4	$182.91	12.771%	$206.2694	$206.27	$206.25	$206.30
Purchase #5	$199.97	4.141%	$208.2508	$208.25	$208.25	$208.30
Purchase #6	$80.54	12.753%	$90.8113	$90.81	$90.80	$90.80
Purchase #7	$245.62	8.838%	$267.3279	$267.33	$267.35	$267.30
7 purchase totals =	$1,033.36		$1,132.4576	$1,132.46	$1,132.40	$1,132.50