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	$109.68	12.312%	$123.1838	$123.18	$123.20	$123.20
Purchase #2	$163.26	6.611%	$174.0531	$174.05	$174.05	$174.10
Purchase #3	$47.65	10.492%	$52.6494	$52.65	$52.65	$52.60
Purchase #4	$198.31	5.555%	$209.3261	$209.33	$209.35	$209.30
Purchase #5	$195.53	7.235%	$209.6766	$209.68	$209.70	$209.70
Purchase #6	$223.45	11.538%	$249.2317	$249.23	$249.25	$249.20
Purchase #7	$116.54	9.245%	$127.3141	$127.31	$127.30	$127.30
7 purchase totals =	$1,054.42		$1,145.4348	$1,145.43	$1,145.50	$1,145.40