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	$126.42	12.456%	$142.1669	$142.17	$142.15	$142.20
Purchase #2	$57.90	12.620%	$65.207	$65.21	$65.20	$65.20
Purchase #3	$45.72	12.162%	$51.2805	$51.28	$51.30	$51.30
Purchase #4	$80.64	7.648%	$86.8073	$86.81	$86.80	$86.80
Purchase #5	$114.58	13.249%	$129.7607	$129.76	$129.75	$129.80
Purchase #6	$130.68	12.172%	$146.5864	$146.59	$146.60	$146.60
Purchase #7	$169.81	9.127%	$185.3086	$185.31	$185.30	$185.30
7 purchase totals =	$725.75		$807.1174	$807.13	$807.10	$807.20