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	$75.52	9.142%	$82.424	$82.42	$82.40	$82.40
Purchase #2	$154.54	7.602%	$166.2881	$166.29	$166.30	$166.30
Purchase #3	$13.28	8.802%	$14.4489	$14.45	$14.45	$14.40
Purchase #4	$209.65	5.342%	$220.8495	$220.85	$220.85	$220.80
Purchase #5	$92.53	7.471%	$99.4429	$99.44	$99.45	$99.40
Purchase #6	$242.50	13.179%	$274.4591	$274.46	$274.45	$274.50
Purchase #7	$62.81	5.715%	$66.3996	$66.40	$66.40	$66.40
7 purchase totals =	$850.83		$924.3121	$924.31	$924.30	$924.20