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	$215.93	10.286%	$238.1406	$238.14	$238.15	$238.10
Purchase #2	$30.88	7.870%	$33.3103	$33.31	$33.30	$33.30
Purchase #3	$158.26	9.258%	$172.9117	$172.91	$172.90	$172.90
Purchase #4	$48.60	7.182%	$52.0905	$52.09	$52.10	$52.10
Purchase #5	$80.86	12.583%	$91.0346	$91.03	$91.05	$91.00
Purchase #6	$33.33	11.134%	$37.041	$37.04	$37.05	$37.00
Purchase #7	$20.62	3.158%	$21.2712	$21.27	$21.25	$21.30
7 purchase totals =	$588.48		$645.7999	$645.79	$645.80	$645.70