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	$28.82	3.734%	$29.8961	$29.90	$29.90	$29.90
Purchase #2	$233.88	9.486%	$256.0659	$256.07	$256.05	$256.10
Purchase #3	$157.70	6.759%	$168.3589	$168.36	$168.35	$168.40
Purchase #4	$123.66	5.503%	$130.465	$130.47	$130.45	$130.50
Purchase #5	$94.85	9.389%	$103.7555	$103.76	$103.75	$103.80
Purchase #6	$181.89	4.370%	$189.8386	$189.84	$189.85	$189.80
Purchase #7	$81.67	9.313%	$89.2759	$89.28	$89.30	$89.30
7 purchase totals =	$902.47		$967.6559	$967.68	$967.65	$967.80