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	$242.52	6.154%	$257.4447	$257.44	$257.45	$257.40
Purchase #2	$56.45	11.375%	$62.8712	$62.87	$62.85	$62.90
Purchase #3	$18.45	12.503%	$20.7568	$20.76	$20.75	$20.80
Purchase #4	$231.91	9.260%	$253.3849	$253.38	$253.40	$253.40
Purchase #5	$70.84	10.646%	$78.3816	$78.38	$78.40	$78.40
Purchase #6	$99.84	8.690%	$108.5161	$108.52	$108.50	$108.50
Purchase #7	$191.94	11.205%	$213.4469	$213.45	$213.45	$213.40
7 purchase totals =	$911.95		$994.8022	$994.80	$994.80	$994.80