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	$241.42	5.856%	$255.5576	$255.56	$255.55	$255.60
Purchase #2	$115.80	4.391%	$120.8848	$120.88	$120.90	$120.90
Purchase #3	$205.98	13.670%	$234.1375	$234.14	$234.15	$234.10
Purchase #4	$75.46	11.849%	$84.4013	$84.40	$84.40	$84.40
Purchase #5	$106.73	4.598%	$111.6374	$111.64	$111.65	$111.60
Purchase #6	$180.59	8.832%	$196.5397	$196.54	$196.55	$196.50
Purchase #7	$59.35	4.682%	$62.1288	$62.13	$62.15	$62.10
7 purchase totals =	$985.33		$1,065.2871	$1,065.29	$1,065.35	$1,065.20