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	$185.34	13.417%	$210.2071	$210.21	$210.20	$210.20
Purchase #2	$51.99	6.851%	$55.5518	$55.55	$55.55	$55.60
Purchase #3	$240.48	8.502%	$260.9256	$260.93	$260.95	$260.90
Purchase #4	$94.53	9.387%	$103.4035	$103.40	$103.40	$103.40
Purchase #5	$200.95	13.342%	$227.7607	$227.76	$227.75	$227.80
Purchase #6	$152.70	13.182%	$172.8289	$172.83	$172.85	$172.80
Purchase #7	$210.26	5.766%	$222.3836	$222.38	$222.40	$222.40
7 purchase totals =	$1,136.25		$1,253.0612	$1,253.06	$1,253.10	$1,253.10