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	$67.77	3.286%	$69.9969	$70.00	$70.00	$70.00
Purchase #2	$194.72	10.841%	$215.8296	$215.83	$215.85	$215.80
Purchase #3	$151.27	10.798%	$167.6041	$167.60	$167.60	$167.60
Purchase #4	$99.94	12.441%	$112.3735	$112.37	$112.35	$112.40
Purchase #5	$170.75	11.527%	$190.4324	$190.43	$190.45	$190.40
Purchase #6	$53.39	9.411%	$58.4145	$58.41	$58.40	$58.40
Purchase #7	$234.79	3.416%	$242.8104	$242.81	$242.80	$242.80
7 purchase totals =	$972.63		$1,057.4614	$1,057.45	$1,057.45	$1,057.40