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	$97.28	8.187%	$105.2443	$105.24	$105.25	$105.20
Purchase #2	$194.38	5.750%	$205.5569	$205.56	$205.55	$205.60
Purchase #3	$194.68	10.801%	$215.7074	$215.71	$215.70	$215.70
Purchase #4	$79.64	13.583%	$90.4575	$90.46	$90.45	$90.50
Purchase #5	$157.95	4.239%	$164.6455	$164.65	$164.65	$164.60
Purchase #6	$80.39	11.221%	$89.4106	$89.41	$89.40	$89.40
Purchase #7	$110.80	11.782%	$123.8545	$123.85	$123.85	$123.90
7 purchase totals =	$915.12		$994.8767	$994.88	$994.85	$994.90