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	$20.81	5.318%	$21.9167	$21.92	$21.90	$21.90
Purchase #2	$135.96	6.431%	$144.7036	$144.70	$144.70	$144.70
Purchase #3	$72.44	13.729%	$82.3853	$82.39	$82.40	$82.40
Purchase #4	$93.83	10.592%	$103.7685	$103.77	$103.75	$103.80
Purchase #5	$55.85	4.805%	$58.5336	$58.53	$58.55	$58.50
Purchase #6	$72.70	12.826%	$82.0245	$82.02	$82.00	$82.00
Purchase #7	$236.25	4.805%	$247.6018	$247.60	$247.60	$247.60
7 purchase totals =	$687.84		$740.9340	$740.93	$740.90	$740.90