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	$72.54	10.750%	$80.3381	$80.34	$80.35	$80.30
Purchase #2	$92.48	9.174%	$100.9641	$100.96	$100.95	$101.00
Purchase #3	$236.78	12.865%	$267.2417	$267.24	$267.25	$267.20
Purchase #4	$75.41	10.860%	$83.5995	$83.60	$83.60	$83.60
Purchase #5	$248.64	12.814%	$280.5007	$280.50	$280.50	$280.50
Purchase #6	$100.54	11.692%	$112.2951	$112.30	$112.30	$112.30
Purchase #7	$25.58	6.862%	$27.3353	$27.34	$27.35	$27.30
7 purchase totals =	$851.97		$952.2745	$952.28	$952.30	$952.20