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	$145.55	7.774%	$156.8651	$156.87	$156.85	$156.90
Purchase #2	$120.81	5.562%	$127.5295	$127.53	$127.55	$127.50
Purchase #3	$88.70	13.710%	$100.8608	$100.86	$100.85	$100.90
Purchase #4	$98.39	3.423%	$101.7579	$101.76	$101.75	$101.80
Purchase #5	$34.31	11.429%	$38.2313	$38.23	$38.25	$38.20
Purchase #6	$248.86	7.126%	$266.5938	$266.59	$266.60	$266.60
Purchase #7	$59.48	10.679%	$65.8319	$65.83	$65.85	$65.80
7 purchase totals =	$796.10		$857.6703	$857.67	$857.70	$857.70