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	$236.96	12.320%	$266.1535	$266.15	$266.15	$266.20
Purchase #2	$130.90	5.830%	$138.5315	$138.53	$138.55	$138.50
Purchase #3	$67.27	9.625%	$73.7447	$73.74	$73.75	$73.70
Purchase #4	$45.61	9.794%	$50.077	$50.08	$50.10	$50.10
Purchase #5	$244.66	4.551%	$255.7945	$255.79	$255.80	$255.80
Purchase #6	$178.87	3.523%	$185.1716	$185.17	$185.15	$185.20
Purchase #7	$190.90	10.219%	$210.4081	$210.41	$210.40	$210.40
7 purchase totals =	$1,095.17		$1,179.8809	$1,179.87	$1,179.90	$1,179.90