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	$213.85	13.370%	$242.4417	$242.44	$242.45	$242.40
Purchase #2	$55.27	8.355%	$59.8878	$59.89	$59.90	$59.90
Purchase #3	$230.99	9.202%	$252.2457	$252.25	$252.25	$252.20
Purchase #4	$101.79	11.765%	$113.7656	$113.77	$113.75	$113.80
Purchase #5	$48.81	11.601%	$54.4724	$54.47	$54.45	$54.50
Purchase #6	$39.27	8.763%	$42.7112	$42.71	$42.70	$42.70
Purchase #7	$243.40	12.703%	$274.3191	$274.32	$274.30	$274.30
7 purchase totals =	$933.38		$1,039.8435	$1,039.85	$1,039.80	$1,039.80