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	$137.85	9.406%	$150.8162	$150.82	$150.80	$150.80
Purchase #2	$249.67	11.359%	$278.03	$278.03	$278.05	$278.00
Purchase #3	$11.76	12.737%	$13.2579	$13.26	$13.25	$13.30
Purchase #4	$94.52	12.124%	$105.9796	$105.98	$106.00	$106.00
Purchase #5	$59.91	12.400%	$67.3388	$67.34	$67.35	$67.30
Purchase #6	$121.42	5.370%	$127.9403	$127.94	$127.95	$127.90
Purchase #7	$124.25	4.824%	$130.2438	$130.24	$130.25	$130.20
7 purchase totals =	$799.38		$873.6066	$873.61	$873.65	$873.50