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	$170.61	4.164%	$177.7142	$177.71	$177.70	$177.70
Purchase #2	$34.78	10.391%	$38.394	$38.39	$38.40	$38.40
Purchase #3	$28.27	5.133%	$29.7211	$29.72	$29.70	$29.70
Purchase #4	$103.26	13.285%	$116.9781	$116.98	$117.00	$117.00
Purchase #5	$73.31	6.549%	$78.1111	$78.11	$78.10	$78.10
Purchase #6	$54.29	12.404%	$61.0241	$61.02	$61.00	$61.00
Purchase #7	$229.41	4.108%	$238.8342	$238.83	$238.85	$238.80
7 purchase totals =	$693.93		$740.7768	$740.76	$740.75	$740.70