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	$29.69	13.808%	$33.7896	$33.79	$33.80	$33.80
Purchase #2	$59.77	4.855%	$62.6718	$62.67	$62.65	$62.70
Purchase #3	$165.89	8.340%	$179.7252	$179.73	$179.75	$179.70
Purchase #4	$101.56	13.549%	$115.3204	$115.32	$115.30	$115.30
Purchase #5	$20.34	11.115%	$22.6008	$22.60	$22.60	$22.60
Purchase #6	$21.82	10.172%	$24.0395	$24.04	$24.05	$24.00
Purchase #7	$208.25	11.305%	$231.7927	$231.79	$231.80	$231.80
7 purchase totals =	$607.32		$669.9400	$669.94	$669.95	$669.90