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	$72.85	10.418%	$80.4395	$80.44	$80.45	$80.40
Purchase #2	$151.85	13.639%	$172.5608	$172.56	$172.55	$172.60
Purchase #3	$140.60	3.686%	$145.7825	$145.78	$145.80	$145.80
Purchase #4	$53.69	6.741%	$57.3092	$57.31	$57.30	$57.30
Purchase #5	$58.25	6.181%	$61.8504	$61.85	$61.85	$61.90
Purchase #6	$195.92	10.373%	$216.2428	$216.24	$216.25	$216.20
Purchase #7	$51.94	4.657%	$54.3588	$54.36	$54.35	$54.40
7 purchase totals =	$725.10		$788.5440	$788.54	$788.55	$788.60