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	$107.84	11.616%	$120.3667	$120.37	$120.35	$120.40
Purchase #2	$243.88	6.768%	$260.3858	$260.39	$260.40	$260.40
Purchase #3	$47.59	5.357%	$50.1394	$50.14	$50.15	$50.10
Purchase #4	$48.72	10.752%	$53.9584	$53.96	$53.95	$54.00
Purchase #5	$33.89	10.627%	$37.4915	$37.49	$37.50	$37.50
Purchase #6	$213.90	10.185%	$235.6857	$235.69	$235.70	$235.70
Purchase #7	$40.49	5.597%	$42.7562	$42.76	$42.75	$42.80
7 purchase totals =	$736.31		$800.7837	$800.80	$800.80	$800.90