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	$222.97	12.289%	$250.3708	$250.37	$250.35	$250.40
Purchase #2	$83.87	8.312%	$90.8413	$90.84	$90.85	$90.80
Purchase #3	$134.92	7.455%	$144.9783	$144.98	$145.00	$145.00
Purchase #4	$208.41	11.202%	$231.7561	$231.76	$231.75	$231.80
Purchase #5	$57.64	4.158%	$60.0367	$60.04	$60.05	$60.00
Purchase #6	$172.89	10.455%	$190.9656	$190.97	$190.95	$191.00
Purchase #7	$40.59	6.604%	$43.2706	$43.27	$43.25	$43.30
7 purchase totals =	$921.29		$1,012.2194	$1,012.23	$1,012.20	$1,012.30