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	$231.50	10.252%	$255.2334	$255.23	$255.25	$255.20
Purchase #2	$172.29	7.792%	$185.7148	$185.71	$185.70	$185.70
Purchase #3	$7.66	10.474%	$8.4623	$8.46	$8.45	$8.50
Purchase #4	$133.42	7.514%	$143.4452	$143.45	$143.45	$143.40
Purchase #5	$191.74	7.694%	$206.4925	$206.49	$206.50	$206.50
Purchase #6	$67.28	11.713%	$75.1605	$75.16	$75.15	$75.20
Purchase #7	$171.53	9.187%	$187.2885	$187.29	$187.30	$187.30
7 purchase totals =	$975.42		$1,061.7972	$1,061.79	$1,061.80	$1,061.80