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	$140.60	9.800%	$154.3788	$154.38	$154.40	$154.40
Purchase #2	$120.67	4.595%	$126.2148	$126.21	$126.20	$126.20
Purchase #3	$239.38	10.425%	$264.3354	$264.34	$264.35	$264.30
Purchase #4	$35.66	13.488%	$40.4698	$40.47	$40.45	$40.50
Purchase #5	$161.30	8.852%	$175.5783	$175.58	$175.60	$175.60
Purchase #6	$80.72	7.254%	$86.5754	$86.58	$86.60	$86.60
Purchase #7	$84.45	7.544%	$90.8209	$90.82	$90.80	$90.80
7 purchase totals =	$862.78		$938.3734	$938.38	$938.40	$938.40