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	$85.96	6.748%	$91.7606	$91.76	$91.75	$91.80
Purchase #2	$217.88	9.804%	$239.241	$239.24	$239.25	$239.20
Purchase #3	$99.26	6.401%	$105.6136	$105.61	$105.60	$105.60
Purchase #4	$124.49	5.661%	$131.5374	$131.54	$131.55	$131.50
Purchase #5	$34.69	13.615%	$39.413	$39.41	$39.40	$39.40
Purchase #6	$59.47	4.389%	$62.0801	$62.08	$62.10	$62.10
Purchase #7	$157.58	8.381%	$170.7868	$170.79	$170.80	$170.80
7 purchase totals =	$779.33		$840.4325	$840.43	$840.45	$840.40