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	$19.92	12.138%	$22.3379	$22.34	$22.35	$22.30
Purchase #2	$132.98	4.492%	$138.9535	$138.95	$138.95	$139.00
Purchase #3	$86.86	3.483%	$89.8853	$89.89	$89.90	$89.90
Purchase #4	$196.67	12.515%	$221.2833	$221.28	$221.30	$221.30
Purchase #5	$200.96	5.257%	$211.5245	$211.52	$211.50	$211.50
Purchase #6	$138.77	3.578%	$143.7352	$143.74	$143.75	$143.70
Purchase #7	$95.73	7.295%	$102.7135	$102.71	$102.70	$102.70
7 purchase totals =	$871.89		$930.4332	$930.43	$930.45	$930.40