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	$103.30	13.636%	$117.386	$117.39	$117.40	$117.40
Purchase #2	$227.32	7.601%	$244.5986	$244.60	$244.60	$244.60
Purchase #3	$217.60	11.401%	$242.4086	$242.41	$242.40	$242.40
Purchase #4	$99.90	9.401%	$109.2916	$109.29	$109.30	$109.30
Purchase #5	$17.58	7.277%	$18.8593	$18.86	$18.85	$18.90
Purchase #6	$20.49	11.118%	$22.7681	$22.77	$22.75	$22.80
Purchase #7	$140.86	13.199%	$159.4521	$159.45	$159.45	$159.50
7 purchase totals =	$827.05		$914.7643	$914.77	$914.75	$914.90