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	$37.26	8.551%	$40.4461	$40.45	$40.45	$40.40
Purchase #2	$144.98	13.209%	$164.1304	$164.13	$164.15	$164.10
Purchase #3	$227.55	12.480%	$255.9482	$255.95	$255.95	$255.90
Purchase #4	$104.82	3.871%	$108.8776	$108.88	$108.90	$108.90
Purchase #5	$116.76	10.331%	$128.8225	$128.82	$128.80	$128.80
Purchase #6	$100.66	10.858%	$111.5897	$111.59	$111.60	$111.60
Purchase #7	$191.53	13.765%	$217.8941	$217.89	$217.90	$217.90
7 purchase totals =	$923.56		$1,027.7086	$1,027.71	$1,027.75	$1,027.60