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	$53.47	4.658%	$55.9606	$55.96	$55.95	$56.00
Purchase #2	$141.73	13.194%	$160.4299	$160.43	$160.45	$160.40
Purchase #3	$6.65	8.617%	$7.223	$7.22	$7.20	$7.20
Purchase #4	$83.27	3.603%	$86.2702	$86.27	$86.25	$86.30
Purchase #5	$217.58	10.666%	$240.7871	$240.79	$240.80	$240.80
Purchase #6	$65.32	10.785%	$72.3648	$72.36	$72.35	$72.40
Purchase #7	$112.73	5.783%	$119.2492	$119.25	$119.25	$119.20
7 purchase totals =	$680.75		$742.2848	$742.28	$742.25	$742.30