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	$44.71	12.694%	$50.3855	$50.39	$50.40	$50.40
Purchase #2	$76.80	3.465%	$79.4611	$79.46	$79.45	$79.50
Purchase #3	$83.87	4.628%	$87.7515	$87.75	$87.75	$87.80
Purchase #4	$100.62	9.166%	$109.8428	$109.84	$109.85	$109.80
Purchase #5	$87.83	9.457%	$96.1361	$96.14	$96.15	$96.10
Purchase #6	$155.60	8.502%	$168.8291	$168.83	$168.85	$168.80
Purchase #7	$51.65	9.401%	$56.5056	$56.51	$56.50	$56.50
7 purchase totals =	$601.08		$648.9117	$648.92	$648.95	$648.90