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	$29.79	8.853%	$32.4273	$32.43	$32.45	$32.40
Purchase #2	$167.78	8.379%	$181.8383	$181.84	$181.85	$181.80
Purchase #3	$78.76	10.754%	$87.2299	$87.23	$87.25	$87.20
Purchase #4	$223.38	13.791%	$254.1863	$254.19	$254.20	$254.20
Purchase #5	$111.46	11.586%	$124.3738	$124.37	$124.35	$124.40
Purchase #6	$103.27	5.459%	$108.9075	$108.91	$108.90	$108.90
Purchase #7	$111.83	10.364%	$123.4201	$123.42	$123.40	$123.40
7 purchase totals =	$826.27		$912.3832	$912.39	$912.40	$912.30