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	$198.34	10.160%	$218.4913	$218.49	$218.50	$218.50
Purchase #2	$174.50	8.130%	$188.6869	$188.69	$188.70	$188.70
Purchase #3	$122.52	7.421%	$131.6122	$131.61	$131.60	$131.60
Purchase #4	$76.85	12.412%	$86.3886	$86.39	$86.40	$86.40
Purchase #5	$70.65	8.686%	$76.7867	$76.79	$76.80	$76.80
Purchase #6	$69.26	10.383%	$76.4513	$76.45	$76.45	$76.50
Purchase #7	$215.49	4.119%	$224.366	$224.37	$224.35	$224.40
7 purchase totals =	$927.61		$1,002.7830	$1,002.79	$1,002.80	$1,002.90