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	$51.39	12.679%	$57.9057	$57.91	$57.90	$57.90
Purchase #2	$132.49	11.151%	$147.264	$147.26	$147.25	$147.30
Purchase #3	$22.94	11.650%	$25.6125	$25.61	$25.60	$25.60
Purchase #4	$134.86	9.872%	$148.1734	$148.17	$148.15	$148.20
Purchase #5	$18.35	9.129%	$20.0252	$20.03	$20.05	$20.00
Purchase #6	$65.99	11.210%	$73.3875	$73.39	$73.40	$73.40
Purchase #7	$238.46	7.176%	$255.5719	$255.57	$255.55	$255.60
7 purchase totals =	$664.48		$727.9402	$727.94	$727.90	$728.00