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	$78.40	5.795%	$82.9433	$82.94	$82.95	$82.90
Purchase #2	$160.45	12.791%	$180.9732	$180.97	$180.95	$181.00
Purchase #3	$199.87	13.284%	$226.4207	$226.42	$226.40	$226.40
Purchase #4	$189.40	3.490%	$196.0101	$196.01	$196.00	$196.00
Purchase #5	$136.28	10.708%	$150.8729	$150.87	$150.85	$150.90
Purchase #6	$11.51	12.117%	$12.9047	$12.90	$12.90	$12.90
Purchase #7	$162.67	4.671%	$170.2683	$170.27	$170.25	$170.30
7 purchase totals =	$938.58		$1,020.3932	$1,020.38	$1,020.30	$1,020.40