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	$25.46	13.698%	$28.9475	$28.95	$28.95	$28.90
Purchase #2	$230.84	11.156%	$256.5925	$256.59	$256.60	$256.60
Purchase #3	$41.90	6.118%	$44.4634	$44.46	$44.45	$44.50
Purchase #4	$145.27	13.676%	$165.1371	$165.14	$165.15	$165.10
Purchase #5	$173.89	5.177%	$182.8923	$182.89	$182.90	$182.90
Purchase #6	$202.52	6.545%	$215.7749	$215.77	$215.75	$215.80
Purchase #7	$120.91	10.874%	$134.0578	$134.06	$134.05	$134.10
7 purchase totals =	$940.79		$1,027.8655	$1,027.86	$1,027.85	$1,027.90