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	$228.71	8.563%	$248.2944	$248.29	$248.30	$248.30
Purchase #2	$71.27	10.635%	$78.8496	$78.85	$78.85	$78.80
Purchase #3	$85.81	3.800%	$89.0708	$89.07	$89.05	$89.10
Purchase #4	$130.82	4.300%	$136.4453	$136.45	$136.45	$136.40
Purchase #5	$51.41	10.206%	$56.6569	$56.66	$56.65	$56.70
Purchase #6	$33.99	7.360%	$36.4917	$36.49	$36.50	$36.50
Purchase #7	$229.75	7.292%	$246.5034	$246.50	$246.50	$246.50
7 purchase totals =	$831.76		$892.3121	$892.31	$892.30	$892.30