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	$219.56	11.825%	$245.523	$245.52	$245.50	$245.50
Purchase #2	$187.66	13.509%	$213.011	$213.01	$213.00	$213.00
Purchase #3	$32.69	9.589%	$35.8246	$35.82	$35.80	$35.80
Purchase #4	$76.66	13.117%	$86.7155	$86.72	$86.70	$86.70
Purchase #5	$181.78	6.503%	$193.6012	$193.60	$193.60	$193.60
Purchase #6	$6.85	8.405%	$7.4257	$7.43	$7.45	$7.40
Purchase #7	$141.37	10.633%	$156.4019	$156.40	$156.40	$156.40
7 purchase totals =	$846.57		$938.5029	$938.50	$938.45	$938.40