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	$229.51	12.504%	$258.2079	$258.21	$258.20	$258.20
Purchase #2	$151.99	10.638%	$168.1587	$168.16	$168.15	$168.20
Purchase #3	$19.58	5.164%	$20.5911	$20.59	$20.60	$20.60
Purchase #4	$156.38	5.691%	$165.2796	$165.28	$165.30	$165.30
Purchase #5	$115.74	3.153%	$119.3893	$119.39	$119.40	$119.40
Purchase #6	$215.82	6.347%	$229.5181	$229.52	$229.50	$229.50
Purchase #7	$161.72	11.743%	$180.7108	$180.71	$180.70	$180.70
7 purchase totals =	$1,050.74		$1,141.8555	$1,141.86	$1,141.85	$1,141.90