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	$230.58	6.596%	$245.7891	$245.79	$245.80	$245.80
Purchase #2	$121.39	5.416%	$127.9645	$127.96	$127.95	$128.00
Purchase #3	$233.88	3.577%	$242.2459	$242.25	$242.25	$242.20
Purchase #4	$80.85	3.551%	$83.721	$83.72	$83.70	$83.70
Purchase #5	$132.96	6.333%	$141.3804	$141.38	$141.40	$141.40
Purchase #6	$21.40	13.582%	$24.3065	$24.31	$24.30	$24.30
Purchase #7	$128.75	10.172%	$141.8465	$141.85	$141.85	$141.80
7 purchase totals =	$949.81		$1,007.2539	$1,007.26	$1,007.25	$1,007.20