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	$135.89	7.802%	$146.4921	$146.49	$146.50	$146.50
Purchase #2	$249.65	10.579%	$276.0605	$276.06	$276.05	$276.10
Purchase #3	$205.42	8.404%	$222.6835	$222.68	$222.70	$222.70
Purchase #4	$71.60	9.818%	$78.6297	$78.63	$78.65	$78.60
Purchase #5	$160.73	7.694%	$173.0966	$173.10	$173.10	$173.10
Purchase #6	$37.68	6.588%	$40.1624	$40.16	$40.15	$40.20
Purchase #7	$78.73	9.315%	$86.0637	$86.06	$86.05	$86.10
7 purchase totals =	$939.70		$1,023.1885	$1,023.18	$1,023.20	$1,023.30