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	$222.33	4.302%	$231.8946	$231.89	$231.90	$231.90
Purchase #2	$157.98	9.211%	$172.5315	$172.53	$172.55	$172.50
Purchase #3	$51.37	5.697%	$54.2965	$54.30	$54.30	$54.30
Purchase #4	$228.89	7.427%	$245.8897	$245.89	$245.90	$245.90
Purchase #5	$149.60	10.532%	$165.3559	$165.36	$165.35	$165.40
Purchase #6	$67.58	10.798%	$74.8773	$74.88	$74.90	$74.90
Purchase #7	$121.27	11.692%	$135.4489	$135.45	$135.45	$135.40
7 purchase totals =	$999.02		$1,080.2944	$1,080.30	$1,080.35	$1,080.30