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	$26.52	11.662%	$29.6128	$29.61	$29.60	$29.60
Purchase #2	$231.93	11.777%	$259.2444	$259.24	$259.25	$259.20
Purchase #3	$237.52	11.757%	$265.4452	$265.45	$265.45	$265.40
Purchase #4	$63.48	13.276%	$71.9076	$71.91	$71.90	$71.90
Purchase #5	$181.44	7.713%	$195.4345	$195.43	$195.45	$195.40
Purchase #6	$179.35	9.703%	$196.7523	$196.75	$196.75	$196.80
Purchase #7	$119.72	6.493%	$127.4934	$127.49	$127.50	$127.50
7 purchase totals =	$1,039.96		$1,145.8902	$1,145.88	$1,145.90	$1,145.80