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	$242.28	5.340%	$255.2178	$255.22	$255.20	$255.20
Purchase #2	$209.50	3.147%	$216.093	$216.09	$216.10	$216.10
Purchase #3	$35.50	8.181%	$38.4043	$38.40	$38.40	$38.40
Purchase #4	$50.96	4.187%	$53.0937	$53.09	$53.10	$53.10
Purchase #5	$159.67	12.541%	$179.6942	$179.69	$179.70	$179.70
Purchase #6	$50.80	7.739%	$54.7314	$54.73	$54.75	$54.70
Purchase #7	$159.82	11.570%	$178.3112	$178.31	$178.30	$178.30
7 purchase totals =	$908.53		$975.5456	$975.53	$975.55	$975.50