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	$127.30	8.344%	$137.9219	$137.92	$137.90	$137.90
Purchase #2	$121.96	7.342%	$130.9143	$130.91	$130.90	$130.90
Purchase #3	$149.73	3.802%	$155.4227	$155.42	$155.40	$155.40
Purchase #4	$227.50	5.867%	$240.8474	$240.85	$240.85	$240.80
Purchase #5	$248.56	12.830%	$280.4502	$280.45	$280.45	$280.50
Purchase #6	$81.42	9.860%	$89.448	$89.45	$89.45	$89.40
Purchase #7	$31.58	3.269%	$32.6124	$32.61	$32.60	$32.60
7 purchase totals =	$988.05		$1,067.6169	$1,067.61	$1,067.55	$1,067.50