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	$104.98	4.425%	$109.6254	$109.63	$109.65	$109.60
Purchase #2	$122.53	4.557%	$128.1137	$128.11	$128.10	$128.10
Purchase #3	$124.71	9.701%	$136.8081	$136.81	$136.80	$136.80
Purchase #4	$129.39	13.164%	$146.4229	$146.42	$146.40	$146.40
Purchase #5	$45.83	5.770%	$48.4744	$48.47	$48.45	$48.50
Purchase #6	$89.94	4.824%	$94.2787	$94.28	$94.30	$94.30
Purchase #7	$22.50	7.288%	$24.1398	$24.14	$24.15	$24.10
7 purchase totals =	$639.88		$687.8630	$687.86	$687.85	$687.80