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	$231.45	6.759%	$247.0937	$247.09	$247.10	$247.10
Purchase #2	$174.60	12.577%	$196.5594	$196.56	$196.55	$196.60
Purchase #3	$157.86	3.465%	$163.3298	$163.33	$163.35	$163.30
Purchase #4	$229.36	13.193%	$259.6195	$259.62	$259.60	$259.60
Purchase #5	$205.83	11.292%	$229.0723	$229.07	$229.05	$229.10
Purchase #6	$135.45	3.573%	$140.2896	$140.29	$140.30	$140.30
Purchase #7	$65.80	10.286%	$72.5682	$72.57	$72.55	$72.60
7 purchase totals =	$1,200.35		$1,308.5325	$1,308.53	$1,308.50	$1,308.60