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	$151.86	3.239%	$156.7787	$156.78	$156.80	$156.80
Purchase #2	$233.58	9.237%	$255.1558	$255.16	$255.15	$255.20
Purchase #3	$172.87	6.732%	$184.5076	$184.51	$184.50	$184.50
Purchase #4	$242.49	8.119%	$262.1778	$262.18	$262.20	$262.20
Purchase #5	$196.54	11.109%	$218.3736	$218.37	$218.35	$218.40
Purchase #6	$79.74	11.368%	$88.8048	$88.80	$88.80	$88.80
Purchase #7	$55.87	6.240%	$59.3563	$59.36	$59.35	$59.40
7 purchase totals =	$1,132.95		$1,225.1546	$1,225.16	$1,225.15	$1,225.30