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	$6.52	6.776%	$6.9618	$6.96	$6.95	$7.00
Purchase #2	$52.75	5.383%	$55.5895	$55.59	$55.60	$55.60
Purchase #3	$154.38	6.509%	$164.4286	$164.43	$164.45	$164.40
Purchase #4	$90.96	12.459%	$102.2927	$102.29	$102.30	$102.30
Purchase #5	$199.75	10.798%	$221.319	$221.32	$221.30	$221.30
Purchase #6	$154.89	6.673%	$165.2258	$165.23	$165.25	$165.20
Purchase #7	$156.99	11.378%	$174.8523	$174.85	$174.85	$174.90
7 purchase totals =	$816.24		$890.6697	$890.67	$890.70	$890.70