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	$63.59	13.226%	$72.0004	$72.00	$72.00	$72.00
Purchase #2	$59.52	11.726%	$66.4993	$66.50	$66.50	$66.50
Purchase #3	$162.30	10.194%	$178.8449	$178.84	$178.85	$178.80
Purchase #4	$99.95	3.861%	$103.8091	$103.81	$103.80	$103.80
Purchase #5	$156.55	7.464%	$168.2349	$168.23	$168.25	$168.20
Purchase #6	$105.64	10.288%	$116.5082	$116.51	$116.50	$116.50
Purchase #7	$81.56	10.335%	$89.9892	$89.99	$90.00	$90.00
7 purchase totals =	$729.11		$795.8860	$795.88	$795.90	$795.80