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	$213.59	3.618%	$221.3177	$221.32	$221.30	$221.30
Purchase #2	$193.71	6.274%	$205.8634	$205.86	$205.85	$205.90
Purchase #3	$174.49	7.319%	$187.2609	$187.26	$187.25	$187.30
Purchase #4	$95.35	8.768%	$103.7103	$103.71	$103.70	$103.70
Purchase #5	$136.56	3.701%	$141.6141	$141.61	$141.60	$141.60
Purchase #6	$40.38	13.294%	$45.7481	$45.75	$45.75	$45.70
Purchase #7	$55.30	7.303%	$59.3386	$59.34	$59.35	$59.30
7 purchase totals =	$909.38		$964.8531	$964.85	$964.80	$964.80