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	$37.94	6.241%	$40.3078	$40.31	$40.30	$40.30
Purchase #2	$242.43	5.756%	$256.3843	$256.38	$256.40	$256.40
Purchase #3	$27.75	10.662%	$30.7087	$30.71	$30.70	$30.70
Purchase #4	$219.47	6.405%	$233.5271	$233.53	$233.55	$233.50
Purchase #5	$124.71	3.329%	$128.8616	$128.86	$128.85	$128.90
Purchase #6	$94.74	11.356%	$105.4987	$105.50	$105.50	$105.50
Purchase #7	$203.50	10.262%	$224.3832	$224.38	$224.40	$224.40
7 purchase totals =	$950.54		$1,019.6714	$1,019.67	$1,019.70	$1,019.70