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	$155.40	5.684%	$164.2329	$164.23	$164.25	$164.20
Purchase #2	$104.42	13.558%	$118.5773	$118.58	$118.60	$118.60
Purchase #3	$136.75	10.373%	$150.9351	$150.94	$150.95	$150.90
Purchase #4	$130.34	10.609%	$144.1678	$144.17	$144.15	$144.20
Purchase #5	$7.48	3.314%	$7.7279	$7.73	$7.75	$7.70
Purchase #6	$111.86	13.140%	$126.5584	$126.56	$126.55	$126.60
Purchase #7	$30.95	13.272%	$35.0577	$35.06	$35.05	$35.10
7 purchase totals =	$677.20		$747.2571	$747.27	$747.30	$747.30