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	$123.78	11.398%	$137.8884	$137.89	$137.90	$137.90
Purchase #2	$205.68	10.446%	$227.1653	$227.17	$227.15	$227.20
Purchase #3	$200.95	12.240%	$225.5463	$225.55	$225.55	$225.50
Purchase #4	$208.41	13.833%	$237.2394	$237.24	$237.25	$237.20
Purchase #5	$209.41	11.548%	$233.5927	$233.59	$233.60	$233.60
Purchase #6	$179.90	8.112%	$194.4935	$194.49	$194.50	$194.50
Purchase #7	$212.54	12.358%	$238.8057	$238.81	$238.80	$238.80
7 purchase totals =	$1,340.67		$1,494.7313	$1,494.74	$1,494.75	$1,494.70