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	$61.87	13.610%	$70.2905	$70.29	$70.30	$70.30
Purchase #2	$250.80	9.470%	$274.5508	$274.55	$274.55	$274.60
Purchase #3	$167.40	9.679%	$183.6026	$183.60	$183.60	$183.60
Purchase #4	$172.59	6.277%	$183.4235	$183.42	$183.40	$183.40
Purchase #5	$116.41	7.317%	$124.9277	$124.93	$124.95	$124.90
Purchase #6	$145.44	3.276%	$150.2046	$150.20	$150.20	$150.20
Purchase #7	$104.72	4.454%	$109.3842	$109.38	$109.40	$109.40
7 purchase totals =	$1,019.23		$1,096.3839	$1,096.37	$1,096.40	$1,096.40