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	$28.68	7.456%	$30.8184	$30.82	$30.80	$30.80
Purchase #2	$141.81	10.168%	$156.2292	$156.23	$156.25	$156.20
Purchase #3	$222.71	12.283%	$250.0655	$250.07	$250.05	$250.10
Purchase #4	$163.39	12.166%	$183.268	$183.27	$183.25	$183.30
Purchase #5	$109.59	9.171%	$119.6405	$119.64	$119.65	$119.60
Purchase #6	$89.32	7.321%	$95.8591	$95.86	$95.85	$95.90
Purchase #7	$226.59	10.384%	$250.1191	$250.12	$250.10	$250.10
7 purchase totals =	$982.09		$1,085.9998	$1,086.01	$1,085.95	$1,086.00