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	$89.25	9.117%	$97.3869	$97.39	$97.40	$97.40
Purchase #2	$248.63	9.362%	$271.9067	$271.91	$271.90	$271.90
Purchase #3	$100.43	10.728%	$111.2041	$111.20	$111.20	$111.20
Purchase #4	$70.36	4.827%	$73.7563	$73.76	$73.75	$73.80
Purchase #5	$31.82	8.164%	$34.4178	$34.42	$34.40	$34.40
Purchase #6	$216.47	10.156%	$238.4547	$238.45	$238.45	$238.50
Purchase #7	$157.81	5.242%	$166.0824	$166.08	$166.10	$166.10
7 purchase totals =	$914.77		$993.2089	$993.21	$993.20	$993.30