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	$25.77	6.645%	$27.4824	$27.48	$27.50	$27.50
Purchase #2	$201.46	10.262%	$222.1338	$222.13	$222.15	$222.10
Purchase #3	$105.76	12.427%	$118.9028	$118.90	$118.90	$118.90
Purchase #4	$104.92	5.802%	$111.0075	$111.01	$111.00	$111.00
Purchase #5	$216.49	10.114%	$238.3858	$238.39	$238.40	$238.40
Purchase #6	$128.53	3.391%	$132.8885	$132.89	$132.90	$132.90
Purchase #7	$59.47	10.591%	$65.7685	$65.77	$65.75	$65.80
7 purchase totals =	$842.40		$916.5693	$916.57	$916.60	$916.60