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	$128.39	4.693%	$134.4153	$134.42	$134.40	$134.40
Purchase #2	$137.52	3.243%	$141.9798	$141.98	$142.00	$142.00
Purchase #3	$105.40	7.764%	$113.5833	$113.58	$113.60	$113.60
Purchase #4	$178.82	9.804%	$196.3515	$196.35	$196.35	$196.40
Purchase #5	$6.30	6.335%	$6.6991	$6.70	$6.70	$6.70
Purchase #6	$188.65	6.437%	$200.7934	$200.79	$200.80	$200.80
Purchase #7	$71.40	9.400%	$78.1116	$78.11	$78.10	$78.10
7 purchase totals =	$816.48		$871.9340	$871.93	$871.95	$872.00