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	$249.98	11.822%	$279.5326	$279.53	$279.55	$279.50
Purchase #2	$146.74	3.545%	$151.9419	$151.94	$151.95	$151.90
Purchase #3	$91.31	8.671%	$99.2275	$99.23	$99.25	$99.20
Purchase #4	$247.96	11.452%	$276.3564	$276.36	$276.35	$276.40
Purchase #5	$161.63	12.106%	$181.1969	$181.20	$181.20	$181.20
Purchase #6	$30.79	7.115%	$32.9807	$32.98	$33.00	$33.00
Purchase #7	$85.49	6.237%	$90.822	$90.82	$90.80	$90.80
7 purchase totals =	$1,013.90		$1,112.0580	$1,112.06	$1,112.10	$1,112.00