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	$174.81	3.275%	$180.535	$180.54	$180.55	$180.50
Purchase #2	$57.49	4.179%	$59.8925	$59.89	$59.90	$59.90
Purchase #3	$40.57	3.585%	$42.0244	$42.02	$42.00	$42.00
Purchase #4	$105.65	5.143%	$111.0836	$111.08	$111.10	$111.10
Purchase #5	$137.57	7.225%	$147.5094	$147.51	$147.50	$147.50
Purchase #6	$226.51	5.618%	$239.2353	$239.24	$239.25	$239.20
Purchase #7	$161.85	9.181%	$176.7094	$176.71	$176.70	$176.70
7 purchase totals =	$904.45		$956.9896	$956.99	$957.00	$956.90