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	$123.54	11.173%	$137.3431	$137.34	$137.35	$137.30
Purchase #2	$215.94	10.843%	$239.3544	$239.35	$239.35	$239.40
Purchase #3	$192.86	10.470%	$213.0524	$213.05	$213.05	$213.10
Purchase #4	$101.30	9.709%	$111.1352	$111.14	$111.15	$111.10
Purchase #5	$40.30	11.376%	$44.8845	$44.88	$44.90	$44.90
Purchase #6	$79.40	8.710%	$86.3157	$86.32	$86.30	$86.30
Purchase #7	$94.41	5.151%	$99.2731	$99.27	$99.25	$99.30
7 purchase totals =	$847.75		$931.3584	$931.35	$931.35	$931.40