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	$230.41	12.405%	$258.9924	$258.99	$259.00	$259.00
Purchase #2	$82.38	11.595%	$91.932	$91.93	$91.95	$91.90
Purchase #3	$98.95	12.525%	$111.3435	$111.34	$111.35	$111.30
Purchase #4	$64.61	11.707%	$72.1739	$72.17	$72.15	$72.20
Purchase #5	$25.60	3.109%	$26.3959	$26.40	$26.40	$26.40
Purchase #6	$159.93	11.668%	$178.5906	$178.59	$178.60	$178.60
Purchase #7	$213.93	3.775%	$222.0059	$222.01	$222.00	$222.00
7 purchase totals =	$875.81		$961.4342	$961.43	$961.45	$961.40