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	$81.30	6.470%	$86.5601	$86.56	$86.55	$86.60
Purchase #2	$115.47	7.625%	$124.2746	$124.27	$124.25	$124.30
Purchase #3	$19.27	8.573%	$20.922	$20.92	$20.90	$20.90
Purchase #4	$144.79	12.766%	$163.2739	$163.27	$163.25	$163.30
Purchase #5	$84.46	13.828%	$96.1391	$96.14	$96.15	$96.10
Purchase #6	$99.68	6.159%	$105.8193	$105.82	$105.80	$105.80
Purchase #7	$76.72	13.196%	$86.844	$86.84	$86.85	$86.80
7 purchase totals =	$621.69		$683.8330	$683.82	$683.75	$683.80