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	$246.61	9.728%	$270.6002	$270.60	$270.60	$270.60
Purchase #2	$35.61	13.470%	$40.4067	$40.41	$40.40	$40.40
Purchase #3	$233.40	10.671%	$258.3061	$258.31	$258.30	$258.30
Purchase #4	$176.78	3.555%	$183.0645	$183.06	$183.05	$183.10
Purchase #5	$108.90	7.717%	$117.3038	$117.30	$117.30	$117.30
Purchase #6	$148.29	11.111%	$164.7665	$164.77	$164.75	$164.80
Purchase #7	$110.86	4.851%	$116.2378	$116.24	$116.25	$116.20
7 purchase totals =	$1,060.45		$1,150.6856	$1,150.69	$1,150.65	$1,150.70