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	$19.36	3.612%	$20.0593	$20.06	$20.05	$20.10
Purchase #2	$155.29	8.548%	$168.5642	$168.56	$168.55	$168.60
Purchase #3	$85.89	6.434%	$91.4162	$91.42	$91.40	$91.40
Purchase #4	$227.83	5.665%	$240.7366	$240.74	$240.75	$240.70
Purchase #5	$156.77	10.706%	$173.5538	$173.55	$173.55	$173.60
Purchase #6	$171.43	4.639%	$179.3826	$179.38	$179.40	$179.40
Purchase #7	$111.26	6.864%	$118.8969	$118.90	$118.90	$118.90
7 purchase totals =	$927.83		$992.6096	$992.61	$992.60	$992.70