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	$129.88	8.797%	$141.3055	$141.31	$141.30	$141.30
Purchase #2	$108.60	3.798%	$112.7246	$112.72	$112.70	$112.70
Purchase #3	$187.90	6.459%	$200.0365	$200.04	$200.05	$200.00
Purchase #4	$121.36	6.197%	$128.8807	$128.88	$128.90	$128.90
Purchase #5	$52.35	8.746%	$56.9285	$56.93	$56.95	$56.90
Purchase #6	$49.72	5.718%	$52.563	$52.56	$52.55	$52.60
Purchase #7	$96.45	7.632%	$103.8111	$103.81	$103.80	$103.80
7 purchase totals =	$746.26		$796.2499	$796.25	$796.25	$796.20