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	$38.61	4.614%	$40.3915	$40.39	$40.40	$40.40
Purchase #2	$147.71	8.442%	$160.1797	$160.18	$160.20	$160.20
Purchase #3	$54.58	13.457%	$61.9248	$61.92	$61.90	$61.90
Purchase #4	$102.86	13.342%	$116.5836	$116.58	$116.60	$116.60
Purchase #5	$204.42	6.441%	$217.5867	$217.59	$217.60	$217.60
Purchase #6	$184.92	13.311%	$209.5347	$209.53	$209.55	$209.50
Purchase #7	$175.31	7.214%	$187.9569	$187.96	$187.95	$188.00
7 purchase totals =	$908.41		$994.1579	$994.15	$994.20	$994.20