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	$71.31	9.208%	$77.8762	$77.88	$77.90	$77.90
Purchase #2	$47.42	9.714%	$52.0264	$52.03	$52.05	$52.00
Purchase #3	$103.90	7.311%	$111.4961	$111.50	$111.50	$111.50
Purchase #4	$62.50	3.184%	$64.49	$64.49	$64.50	$64.50
Purchase #5	$169.89	5.216%	$178.7515	$178.75	$178.75	$178.80
Purchase #6	$200.80	9.212%	$219.2977	$219.30	$219.30	$219.30
Purchase #7	$213.31	12.664%	$240.3236	$240.32	$240.30	$240.30
7 purchase totals =	$869.13		$944.2615	$944.27	$944.30	$944.30