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	$242.31	5.675%	$256.0611	$256.06	$256.05	$256.10
Purchase #2	$30.53	4.691%	$31.9622	$31.96	$31.95	$32.00
Purchase #3	$16.78	4.231%	$17.49	$17.49	$17.50	$17.50
Purchase #4	$190.37	10.614%	$210.5759	$210.58	$210.60	$210.60
Purchase #5	$20.96	8.418%	$22.7244	$22.72	$22.70	$22.70
Purchase #6	$138.40	7.360%	$148.5862	$148.59	$148.60	$148.60
Purchase #7	$80.98	10.218%	$89.2545	$89.25	$89.25	$89.30
7 purchase totals =	$720.33		$776.6543	$776.65	$776.65	$776.80