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	$68.90	5.288%	$72.5434	$72.54	$72.55	$72.50
Purchase #2	$64.61	9.868%	$70.9857	$70.99	$71.00	$71.00
Purchase #3	$248.89	7.509%	$267.5792	$267.58	$267.60	$267.60
Purchase #4	$43.29	6.317%	$46.0246	$46.02	$46.00	$46.00
Purchase #5	$172.89	10.185%	$190.4988	$190.50	$190.50	$190.50
Purchase #6	$120.61	6.147%	$128.0239	$128.02	$128.00	$128.00
Purchase #7	$48.57	8.666%	$52.7791	$52.78	$52.80	$52.80
7 purchase totals =	$767.76		$828.4347	$828.43	$828.45	$828.40