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	$140.99	6.617%	$150.3193	$150.32	$150.30	$150.30
Purchase #2	$126.37	3.601%	$130.9206	$130.92	$130.90	$130.90
Purchase #3	$107.55	5.811%	$113.7997	$113.80	$113.80	$113.80
Purchase #4	$85.79	12.600%	$96.5995	$96.60	$96.60	$96.60
Purchase #5	$182.76	10.117%	$201.2498	$201.25	$201.25	$201.20
Purchase #6	$105.42	5.844%	$111.5807	$111.58	$111.60	$111.60
Purchase #7	$36.47	11.165%	$40.5419	$40.54	$40.55	$40.50
7 purchase totals =	$785.35		$845.0115	$845.01	$845.00	$844.90