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	$129.49	9.147%	$141.3345	$141.33	$141.35	$141.30
Purchase #2	$219.67	3.473%	$227.2991	$227.30	$227.30	$227.30
Purchase #3	$81.71	9.596%	$89.5509	$89.55	$89.55	$89.60
Purchase #4	$171.86	12.208%	$192.8407	$192.84	$192.85	$192.80
Purchase #5	$204.43	5.152%	$214.9622	$214.96	$214.95	$215.00
Purchase #6	$183.82	9.236%	$200.7976	$200.80	$200.80	$200.80
Purchase #7	$140.91	3.415%	$145.7221	$145.72	$145.70	$145.70
7 purchase totals =	$1,131.89		$1,212.5071	$1,212.50	$1,212.50	$1,212.50