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	$27.58	3.335%	$28.4998	$28.50	$28.50	$28.50
Purchase #2	$69.64	13.626%	$79.1291	$79.13	$79.15	$79.10
Purchase #3	$121.76	9.133%	$132.8803	$132.88	$132.90	$132.90
Purchase #4	$95.98	9.665%	$105.2565	$105.26	$105.25	$105.30
Purchase #5	$135.79	4.119%	$141.3832	$141.38	$141.40	$141.40
Purchase #6	$99.32	9.373%	$108.6293	$108.63	$108.65	$108.60
Purchase #7	$113.44	13.616%	$128.886	$128.89	$128.90	$128.90
7 purchase totals =	$663.51		$724.6642	$724.67	$724.75	$724.70