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	$227.60	8.261%	$246.402	$246.40	$246.40	$246.40
Purchase #2	$31.83	5.459%	$33.5676	$33.57	$33.55	$33.60
Purchase #3	$222.71	8.358%	$241.3241	$241.32	$241.30	$241.30
Purchase #4	$146.59	6.258%	$155.7636	$155.76	$155.75	$155.80
Purchase #5	$126.86	3.432%	$131.2138	$131.21	$131.20	$131.20
Purchase #6	$231.30	11.367%	$257.5919	$257.59	$257.60	$257.60
Purchase #7	$245.60	3.848%	$255.0507	$255.05	$255.05	$255.10
7 purchase totals =	$1,232.49		$1,320.9137	$1,320.90	$1,320.85	$1,321.00