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	$21.78	10.860%	$24.1453	$24.15	$24.15	$24.10
Purchase #2	$194.51	5.240%	$204.7023	$204.70	$204.70	$204.70
Purchase #3	$139.36	4.682%	$145.8848	$145.88	$145.90	$145.90
Purchase #4	$67.32	4.654%	$70.4531	$70.45	$70.45	$70.50
Purchase #5	$128.72	12.478%	$144.7817	$144.78	$144.80	$144.80
Purchase #6	$207.71	10.230%	$228.9587	$228.96	$228.95	$229.00
Purchase #7	$30.31	7.319%	$32.5284	$32.53	$32.55	$32.50
7 purchase totals =	$789.71		$851.4543	$851.45	$851.50	$851.50