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	$128.52	10.654%	$142.2125	$142.21	$142.20	$142.20
Purchase #2	$219.52	8.830%	$238.9036	$238.90	$238.90	$238.90
Purchase #3	$171.86	3.334%	$177.5898	$177.59	$177.60	$177.60
Purchase #4	$235.43	12.411%	$264.6492	$264.65	$264.65	$264.60
Purchase #5	$5.39	7.717%	$5.8059	$5.81	$5.80	$5.80
Purchase #6	$173.26	9.826%	$190.2845	$190.28	$190.30	$190.30
Purchase #7	$166.84	3.321%	$172.3808	$172.38	$172.40	$172.40
7 purchase totals =	$1,100.82		$1,191.8263	$1,191.82	$1,191.85	$1,191.80