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	$123.42	11.672%	$137.8256	$137.83	$137.85	$137.80
Purchase #2	$129.85	11.170%	$144.3542	$144.35	$144.35	$144.40
Purchase #3	$29.74	10.309%	$32.8059	$32.81	$32.80	$32.80
Purchase #4	$44.97	12.333%	$50.5162	$50.52	$50.50	$50.50
Purchase #5	$202.34	10.656%	$223.9014	$223.90	$223.90	$223.90
Purchase #6	$18.78	9.260%	$20.519	$20.52	$20.50	$20.50
Purchase #7	$92.77	9.305%	$101.4022	$101.40	$101.40	$101.40
7 purchase totals =	$641.87		$711.3245	$711.33	$711.30	$711.30