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	$177.33	11.661%	$198.0085	$198.01	$198.00	$198.00
Purchase #2	$66.86	9.378%	$73.1301	$73.13	$73.15	$73.10
Purchase #3	$96.36	3.395%	$99.6314	$99.63	$99.65	$99.60
Purchase #4	$123.72	5.211%	$130.167	$130.17	$130.15	$130.20
Purchase #5	$40.32	11.838%	$45.0931	$45.09	$45.10	$45.10
Purchase #6	$100.48	11.313%	$111.8473	$111.85	$111.85	$111.80
Purchase #7	$176.42	3.712%	$182.9687	$182.97	$182.95	$183.00
7 purchase totals =	$781.49		$840.8461	$840.85	$840.85	$840.80