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	$84.45	7.805%	$91.0413	$91.04	$91.05	$91.00
Purchase #2	$90.83	12.252%	$101.9585	$101.96	$101.95	$102.00
Purchase #3	$129.47	3.555%	$134.0727	$134.07	$134.05	$134.10
Purchase #4	$90.73	13.872%	$103.3161	$103.32	$103.30	$103.30
Purchase #5	$15.35	13.367%	$17.4018	$17.40	$17.40	$17.40
Purchase #6	$154.64	6.381%	$164.5076	$164.51	$164.50	$164.50
Purchase #7	$52.52	3.436%	$54.3246	$54.32	$54.30	$54.30
7 purchase totals =	$617.99		$666.6226	$666.62	$666.55	$666.60