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	$132.59	9.259%	$144.8665	$144.87	$144.85	$144.90
Purchase #2	$72.33	4.799%	$75.8011	$75.80	$75.80	$75.80
Purchase #3	$101.56	10.152%	$111.8704	$111.87	$111.85	$111.90
Purchase #4	$92.74	7.129%	$99.3514	$99.35	$99.35	$99.40
Purchase #5	$232.27	6.144%	$246.5407	$246.54	$246.55	$246.50
Purchase #6	$81.93	11.670%	$91.4912	$91.49	$91.50	$91.50
Purchase #7	$96.71	8.663%	$105.088	$105.09	$105.10	$105.10
7 purchase totals =	$810.13		$875.0093	$875.01	$875.00	$875.10