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	$145.51	10.298%	$160.4946	$160.49	$160.50	$160.50
Purchase #2	$85.91	4.256%	$89.5663	$89.57	$89.55	$89.60
Purchase #3	$202.85	3.544%	$210.039	$210.04	$210.05	$210.00
Purchase #4	$168.45	12.390%	$189.321	$189.32	$189.30	$189.30
Purchase #5	$74.93	10.536%	$82.8246	$82.82	$82.80	$82.80
Purchase #6	$8.84	3.573%	$9.1559	$9.16	$9.15	$9.20
Purchase #7	$244.78	5.384%	$257.959	$257.96	$257.95	$258.00
7 purchase totals =	$931.27		$999.3604	$999.36	$999.30	$999.40