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	$6.87	4.118%	$7.1529	$7.15	$7.15	$7.20
Purchase #2	$41.82	7.189%	$44.8264	$44.83	$44.85	$44.80
Purchase #3	$80.94	10.731%	$89.6257	$89.63	$89.65	$89.60
Purchase #4	$51.72	7.813%	$55.7609	$55.76	$55.75	$55.80
Purchase #5	$31.52	13.208%	$35.6832	$35.68	$35.70	$35.70
Purchase #6	$128.89	6.854%	$137.7241	$137.72	$137.70	$137.70
Purchase #7	$38.84	7.736%	$41.8447	$41.84	$41.85	$41.80
7 purchase totals =	$380.60		$412.6179	$412.61	$412.65	$412.60