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	$45.90	6.116%	$48.7072	$48.71	$48.70	$48.70
Purchase #2	$225.37	3.390%	$233.01	$233.01	$233.00	$233.00
Purchase #3	$6.36	9.144%	$6.9416	$6.94	$6.95	$6.90
Purchase #4	$71.96	11.360%	$80.1347	$80.13	$80.15	$80.10
Purchase #5	$215.35	5.428%	$227.0392	$227.04	$227.05	$227.00
Purchase #6	$94.51	6.169%	$100.3403	$100.34	$100.35	$100.30
Purchase #7	$53.47	5.507%	$56.4146	$56.41	$56.40	$56.40
7 purchase totals =	$712.92		$752.5876	$752.58	$752.60	$752.40