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	$82.33	3.720%	$85.3927	$85.39	$85.40	$85.40
Purchase #2	$106.53	7.367%	$114.3781	$114.38	$114.40	$114.40
Purchase #3	$99.92	11.841%	$111.7515	$111.75	$111.75	$111.80
Purchase #4	$76.97	9.468%	$84.2575	$84.26	$84.25	$84.30
Purchase #5	$190.65	9.307%	$208.3938	$208.39	$208.40	$208.40
Purchase #6	$76.54	7.246%	$82.0861	$82.09	$82.10	$82.10
Purchase #7	$101.86	4.375%	$106.3164	$106.32	$106.30	$106.30
7 purchase totals =	$734.80		$792.5761	$792.58	$792.60	$792.70