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	$82.86	3.296%	$85.5911	$85.59	$85.60	$85.60
Purchase #2	$106.37	7.469%	$114.3148	$114.31	$114.30	$114.30
Purchase #3	$82.58	9.679%	$90.5729	$90.57	$90.55	$90.60
Purchase #4	$216.67	6.363%	$230.4567	$230.46	$230.45	$230.50
Purchase #5	$59.57	6.155%	$63.2365	$63.24	$63.25	$63.20
Purchase #6	$114.99	13.667%	$130.7057	$130.71	$130.70	$130.70
Purchase #7	$241.36	13.322%	$273.514	$273.51	$273.50	$273.50
7 purchase totals =	$904.40		$988.3917	$988.39	$988.35	$988.40