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	$21.88	11.104%	$24.3096	$24.31	$24.30	$24.30
Purchase #2	$12.39	9.407%	$13.5555	$13.56	$13.55	$13.60
Purchase #3	$38.99	4.610%	$40.7874	$40.79	$40.80	$40.80
Purchase #4	$119.37	3.154%	$123.1349	$123.13	$123.15	$123.10
Purchase #5	$109.29	9.855%	$120.0605	$120.06	$120.05	$120.10
Purchase #6	$241.38	7.617%	$259.7659	$259.77	$259.75	$259.80
Purchase #7	$67.86	3.498%	$70.2337	$70.23	$70.25	$70.20
7 purchase totals =	$611.16		$651.8475	$651.85	$651.85	$651.90