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	$79.43	13.604%	$90.2357	$90.24	$90.25	$90.20
Purchase #2	$104.35	6.775%	$111.4197	$111.42	$111.40	$111.40
Purchase #3	$29.96	12.388%	$33.6714	$33.67	$33.65	$33.70
Purchase #4	$58.52	6.630%	$62.3999	$62.40	$62.40	$62.40
Purchase #5	$156.47	6.214%	$166.193	$166.19	$166.20	$166.20
Purchase #6	$113.46	9.538%	$124.2818	$124.28	$124.30	$124.30
Purchase #7	$140.99	10.117%	$155.254	$155.25	$155.25	$155.30
7 purchase totals =	$683.18		$743.4555	$743.45	$743.45	$743.50