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	$53.53	6.163%	$56.8291	$56.83	$56.85	$56.80
Purchase #2	$30.74	5.365%	$32.3892	$32.39	$32.40	$32.40
Purchase #3	$28.76	12.616%	$32.3884	$32.39	$32.40	$32.40
Purchase #4	$128.75	11.782%	$143.9193	$143.92	$143.90	$143.90
Purchase #5	$130.94	9.491%	$143.3675	$143.37	$143.35	$143.40
Purchase #6	$19.52	4.314%	$20.3621	$20.36	$20.35	$20.40
Purchase #7	$119.74	4.481%	$125.1055	$125.11	$125.10	$125.10
7 purchase totals =	$511.98		$554.3611	$554.37	$554.35	$554.40