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	$142.40	9.404%	$155.7913	$155.79	$155.80	$155.80
Purchase #2	$228.73	4.425%	$238.8513	$238.85	$238.85	$238.90
Purchase #3	$176.42	6.494%	$187.8767	$187.88	$187.90	$187.90
Purchase #4	$244.42	12.714%	$275.4956	$275.50	$275.50	$275.50
Purchase #5	$179.61	12.647%	$202.3253	$202.33	$202.35	$202.30
Purchase #6	$140.91	11.358%	$156.9146	$156.91	$156.90	$156.90
Purchase #7	$66.91	4.821%	$70.1357	$70.14	$70.15	$70.10
7 purchase totals =	$1,179.40		$1,287.3905	$1,287.40	$1,287.45	$1,287.40