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	$88.90	11.746%	$99.3422	$99.34	$99.35	$99.30
Purchase #2	$202.31	7.553%	$217.5905	$217.59	$217.60	$217.60
Purchase #3	$64.29	9.615%	$70.4715	$70.47	$70.45	$70.50
Purchase #4	$241.86	4.713%	$253.2589	$253.26	$253.25	$253.30
Purchase #5	$188.88	9.194%	$206.2456	$206.25	$206.25	$206.20
Purchase #6	$34.28	12.427%	$38.54	$38.54	$38.55	$38.50
Purchase #7	$17.42	8.719%	$18.9388	$18.94	$18.95	$18.90
7 purchase totals =	$837.94		$904.3875	$904.39	$904.40	$904.30