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	$158.80	8.747%	$172.6902	$172.69	$172.70	$172.70
Purchase #2	$159.36	3.333%	$164.6715	$164.67	$164.65	$164.70
Purchase #3	$103.32	11.561%	$115.2648	$115.26	$115.25	$115.30
Purchase #4	$98.97	12.508%	$111.3492	$111.35	$111.35	$111.30
Purchase #5	$69.87	7.760%	$75.2919	$75.29	$75.30	$75.30
Purchase #6	$75.43	4.287%	$78.6637	$78.66	$78.65	$78.70
Purchase #7	$105.57	12.804%	$119.0872	$119.09	$119.10	$119.10
7 purchase totals =	$771.32		$837.0185	$837.01	$837.00	$837.10