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	$91.65	3.534%	$94.8889	$94.89	$94.90	$94.90
Purchase #2	$29.62	10.649%	$32.7742	$32.77	$32.75	$32.80
Purchase #3	$45.29	6.309%	$48.1473	$48.15	$48.15	$48.10
Purchase #4	$171.66	3.794%	$178.1728	$178.17	$178.15	$178.20
Purchase #5	$55.56	12.194%	$62.335	$62.34	$62.35	$62.30
Purchase #6	$27.40	13.413%	$31.0752	$31.08	$31.10	$31.10
Purchase #7	$47.53	12.241%	$53.3481	$53.35	$53.35	$53.30
7 purchase totals =	$468.71		$500.7415	$500.75	$500.75	$500.70