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	$77.57	4.129%	$80.7729	$80.77	$80.75	$80.80
Purchase #2	$155.47	5.251%	$163.6337	$163.63	$163.65	$163.60
Purchase #3	$229.77	9.213%	$250.9387	$250.94	$250.95	$250.90
Purchase #4	$104.72	6.861%	$111.9048	$111.90	$111.90	$111.90
Purchase #5	$216.84	6.449%	$230.824	$230.82	$230.80	$230.80
Purchase #6	$74.38	10.685%	$82.3275	$82.33	$82.35	$82.30
Purchase #7	$120.80	13.797%	$137.4668	$137.47	$137.45	$137.50
7 purchase totals =	$979.55		$1,057.8684	$1,057.86	$1,057.85	$1,057.80