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	$85.62	5.867%	$90.6433	$90.64	$90.65	$90.60
Purchase #2	$230.89	8.545%	$250.6196	$250.62	$250.60	$250.60
Purchase #3	$128.56	5.711%	$135.9021	$135.90	$135.90	$135.90
Purchase #4	$105.38	10.460%	$116.4027	$116.40	$116.40	$116.40
Purchase #5	$246.81	10.548%	$272.8435	$272.84	$272.85	$272.80
Purchase #6	$72.38	13.687%	$82.2867	$82.29	$82.30	$82.30
Purchase #7	$40.39	10.464%	$44.6164	$44.62	$44.60	$44.60
7 purchase totals =	$910.03		$993.3143	$993.31	$993.30	$993.20