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	$37.81	9.668%	$41.4655	$41.47	$41.45	$41.50
Purchase #2	$144.83	3.789%	$150.3176	$150.32	$150.30	$150.30
Purchase #3	$92.86	6.874%	$99.2432	$99.24	$99.25	$99.20
Purchase #4	$35.81	5.463%	$37.7663	$37.77	$37.75	$37.80
Purchase #5	$90.95	12.380%	$102.2096	$102.21	$102.20	$102.20
Purchase #6	$39.78	5.418%	$41.9353	$41.94	$41.95	$41.90
Purchase #7	$168.81	13.295%	$191.2533	$191.25	$191.25	$191.30
7 purchase totals =	$610.85		$664.1908	$664.20	$664.15	$664.20