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	$98.88	12.821%	$111.5574	$111.56	$111.55	$111.60
Purchase #2	$54.83	3.603%	$56.8055	$56.81	$56.80	$56.80
Purchase #3	$161.96	7.757%	$174.5232	$174.52	$174.50	$174.50
Purchase #4	$18.63	13.431%	$21.1322	$21.13	$21.15	$21.10
Purchase #5	$32.84	7.270%	$35.2275	$35.23	$35.25	$35.20
Purchase #6	$113.80	5.334%	$119.8701	$119.87	$119.85	$119.90
Purchase #7	$32.62	3.843%	$33.8736	$33.87	$33.85	$33.90
7 purchase totals =	$513.56		$552.9895	$552.99	$552.95	$553.00