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	$72.88	12.748%	$82.1707	$82.17	$82.15	$82.20
Purchase #2	$177.82	7.556%	$191.2561	$191.26	$191.25	$191.30
Purchase #3	$118.91	9.114%	$129.7475	$129.75	$129.75	$129.70
Purchase #4	$18.98	3.340%	$19.6139	$19.61	$19.60	$19.60
Purchase #5	$12.40	11.626%	$13.8416	$13.84	$13.85	$13.80
Purchase #6	$189.71	5.372%	$199.9012	$199.90	$199.90	$199.90
Purchase #7	$131.61	11.382%	$146.5899	$146.59	$146.60	$146.60
7 purchase totals =	$722.31		$783.1209	$783.12	$783.10	$783.10