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	$6.32	13.660%	$7.1833	$7.18	$7.20	$7.20
Purchase #2	$19.67	4.188%	$20.4938	$20.49	$20.50	$20.50
Purchase #3	$220.84	8.804%	$240.2828	$240.28	$240.30	$240.30
Purchase #4	$19.98	4.418%	$20.8627	$20.86	$20.85	$20.90
Purchase #5	$123.91	3.758%	$128.5665	$128.57	$128.55	$128.60
Purchase #6	$167.97	8.123%	$181.6142	$181.61	$181.60	$181.60
Purchase #7	$195.45	3.116%	$201.5402	$201.54	$201.55	$201.50
7 purchase totals =	$754.14		$800.5435	$800.53	$800.55	$800.60