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	$115.35	10.268%	$127.1941	$127.19	$127.20	$127.20
Purchase #2	$225.78	12.686%	$254.4225	$254.42	$254.40	$254.40
Purchase #3	$95.40	4.538%	$99.7293	$99.73	$99.75	$99.70
Purchase #4	$236.56	7.307%	$253.8454	$253.85	$253.85	$253.80
Purchase #5	$123.96	6.387%	$131.8773	$131.88	$131.90	$131.90
Purchase #6	$227.59	9.393%	$248.9675	$248.97	$248.95	$249.00
Purchase #7	$167.75	9.403%	$183.5235	$183.52	$183.50	$183.50
7 purchase totals =	$1,192.39		$1,299.5596	$1,299.56	$1,299.55	$1,299.50