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	$99.45	4.642%	$104.0665	$104.07	$104.05	$104.10
Purchase #2	$33.60	13.786%	$38.2321	$38.23	$38.25	$38.20
Purchase #3	$122.41	3.251%	$126.3895	$126.39	$126.40	$126.40
Purchase #4	$146.50	4.345%	$152.8654	$152.87	$152.85	$152.90
Purchase #5	$248.66	10.551%	$274.8961	$274.90	$274.90	$274.90
Purchase #6	$42.93	4.734%	$44.9623	$44.96	$44.95	$45.00
Purchase #7	$231.96	4.526%	$242.4585	$242.46	$242.45	$242.50
7 purchase totals =	$925.51		$983.8704	$983.88	$983.85	$984.00