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	$92.43	13.800%	$105.1853	$105.19	$105.20	$105.20
Purchase #2	$99.45	11.512%	$110.8987	$110.90	$110.90	$110.90
Purchase #3	$97.67	5.373%	$102.9178	$102.92	$102.90	$102.90
Purchase #4	$128.34	10.674%	$142.039	$142.04	$142.05	$142.00
Purchase #5	$40.63	10.185%	$44.7682	$44.77	$44.75	$44.80
Purchase #6	$11.32	13.731%	$12.8743	$12.87	$12.85	$12.90
Purchase #7	$27.47	8.711%	$29.8629	$29.86	$29.85	$29.90
7 purchase totals =	$497.31		$548.5462	$548.55	$548.50	$548.60