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	$240.84	12.172%	$270.155	$270.16	$270.15	$270.20
Purchase #2	$35.43	12.346%	$39.8042	$39.80	$39.80	$39.80
Purchase #3	$177.99	10.429%	$196.5526	$196.55	$196.55	$196.60
Purchase #4	$161.32	10.530%	$178.307	$178.31	$178.30	$178.30
Purchase #5	$183.61	12.697%	$206.923	$206.92	$206.90	$206.90
Purchase #6	$18.67	13.264%	$21.1464	$21.15	$21.15	$21.10
Purchase #7	$240.37	5.418%	$253.3932	$253.39	$253.40	$253.40
7 purchase totals =	$1,058.23		$1,166.2814	$1,166.28	$1,166.25	$1,166.30