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	$69.86	4.641%	$73.1022	$73.10	$73.10	$73.10
Purchase #2	$28.62	12.153%	$32.0982	$32.10	$32.10	$32.10
Purchase #3	$32.61	8.582%	$35.4086	$35.41	$35.40	$35.40
Purchase #4	$138.76	4.774%	$145.3844	$145.38	$145.40	$145.40
Purchase #5	$82.85	7.629%	$89.1706	$89.17	$89.15	$89.20
Purchase #6	$138.52	13.517%	$157.2437	$157.24	$157.25	$157.20
Purchase #7	$101.36	10.155%	$111.6531	$111.65	$111.65	$111.70
7 purchase totals =	$592.58		$644.0608	$644.05	$644.05	$644.10