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	$18.60	3.368%	$19.2264	$19.23	$19.25	$19.20
Purchase #2	$51.94	7.413%	$55.7903	$55.79	$55.80	$55.80
Purchase #3	$59.63	3.192%	$61.5334	$61.53	$61.55	$61.50
Purchase #4	$86.32	6.752%	$92.1483	$92.15	$92.15	$92.10
Purchase #5	$211.50	6.499%	$225.2454	$225.25	$225.25	$225.20
Purchase #6	$95.69	7.307%	$102.6821	$102.68	$102.70	$102.70
Purchase #7	$19.72	5.298%	$20.7648	$20.76	$20.75	$20.80
7 purchase totals =	$543.40		$577.3907	$577.39	$577.45	$577.30