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	$41.98	13.627%	$47.7006	$47.70	$47.70	$47.70
Purchase #2	$203.87	9.312%	$222.8544	$222.85	$222.85	$222.90
Purchase #3	$77.39	11.823%	$86.5398	$86.54	$86.55	$86.50
Purchase #4	$45.47	6.269%	$48.3205	$48.32	$48.30	$48.30
Purchase #5	$57.33	10.720%	$63.4758	$63.48	$63.50	$63.50
Purchase #6	$28.33	7.557%	$30.4709	$30.47	$30.45	$30.50
Purchase #7	$233.72	8.782%	$254.2453	$254.25	$254.25	$254.20
7 purchase totals =	$688.09		$753.6073	$753.61	$753.60	$753.60