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	$80.57	12.450%	$90.601	$90.60	$90.60	$90.60
Purchase #2	$19.84	5.759%	$20.9826	$20.98	$21.00	$21.00
Purchase #3	$122.67	3.797%	$127.3278	$127.33	$127.35	$127.30
Purchase #4	$131.77	9.277%	$143.9943	$143.99	$144.00	$144.00
Purchase #5	$152.32	13.800%	$173.3402	$173.34	$173.35	$173.30
Purchase #6	$206.80	10.148%	$227.7861	$227.79	$227.80	$227.80
Purchase #7	$37.98	12.597%	$42.7643	$42.76	$42.75	$42.80
7 purchase totals =	$751.95		$826.7963	$826.79	$826.85	$826.80