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	$31.34	3.172%	$32.3341	$32.33	$32.35	$32.30
Purchase #2	$135.54	4.432%	$141.5471	$141.55	$141.55	$141.50
Purchase #3	$111.96	3.667%	$116.0656	$116.07	$116.05	$116.10
Purchase #4	$171.60	10.870%	$190.2529	$190.25	$190.25	$190.30
Purchase #5	$155.36	6.852%	$166.0053	$166.01	$166.00	$166.00
Purchase #6	$48.46	9.629%	$53.1262	$53.13	$53.15	$53.10
Purchase #7	$145.26	4.574%	$151.9042	$151.90	$151.90	$151.90
7 purchase totals =	$799.52		$851.2354	$851.24	$851.25	$851.20