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	$66.81	9.182%	$72.9445	$72.94	$72.95	$72.90
Purchase #2	$50.88	11.711%	$56.8386	$56.84	$56.85	$56.80
Purchase #3	$47.82	9.275%	$52.2553	$52.26	$52.25	$52.30
Purchase #4	$84.88	3.474%	$87.8287	$87.83	$87.85	$87.80
Purchase #5	$127.93	11.168%	$142.2172	$142.22	$142.20	$142.20
Purchase #6	$70.25	5.674%	$74.236	$74.24	$74.25	$74.20
Purchase #7	$55.69	11.298%	$61.9819	$61.98	$62.00	$62.00
7 purchase totals =	$504.26		$548.3022	$548.31	$548.35	$548.20